babyNew Year’s Day has long been one of my favorite holidays. It caps a week of year-in-review stories that underscores how ghastly the past year has been – fiscal cliffs, mass shootings, super storms – and then for a few glorious minutes you’re in a crowd of ecstatic people screaming, embracing, giddy again about the possibility, however sketchy, that great things are about to happen.

There is a fine line between delusion and optimism, but Silicon Valley has often had reasons to expect great things – especially in recent years as fertile areas like social networking and the mobile Web offered new opportunity for those willing to work for it. The Web remained a bright spot in a dim economy, and so looking back often meant recounting success stories.

As we exit 2012, something feels different. There’s more caution than hope, a sense that things will get harder for entrepreneurs before they get better. The top stories of 2012 aren’t happy ones: Facebook’s troubled IPO, endless patent fights, the lackluster launch of Windows 8, the late backlash against Apple. It’s not just the weak global economy or the uncertainty about the fiscal future. The Web industry has thrived amid gloom and uncertainty before.

If anything changed in 2012, it was that Silicon Valley in general and the Web sector in particular began to resemble other, older industries. The Web grew up in 2012, in the sense that adulthood is a less magical, playful realm than childhood. Not middle-age adulthood, where growth is stagnant and the future looks gray, but early adulthood where the hard realities of compromise and responsibilities begin to sink in.

The more mainstream Web content becomes, the faster startups seem to reach adulthood. Two years ago, Instagram boasted of 1 million users. Now it has more than 100 million. Facebook’s revenue grew 88 percent last year and 154 percent the year before that. This year, annual growth has slowed to 32 percent. Groupon’s slowdown is even more dramatic: 415 percent revenue growth in 2011, 32 percent growth last quarter.

The shift is evident in the attitudes of investors, who have gone from courting young startups at any cost to acting as if Time’s winged chariot is hurrying near. Through 2012, price-earnings valuations of tech companies are below average: Apple’s PE is 12, Microsoft’s is 14. The average PE for the S&P 500 is 16. Google’s PE is a little higher (18), even though its revenue is expected to grow 42 percent this year.

Younger companies that have gone public recently are doing even worse. Despite recent recoveries, Facebook is down 30 percent from its IPO. Groupon lost 79 percent of its value in 2012, while Zynga lost 75 percent. Not all were busts, to be sure. LinkedIn rose 80 percent in 2012.

Success stories were the exceptions in the public markets this year, not the rule. That rule seemed to be spreading into the private markets as well, inspiring a new sense of caution among venture capitalists as well as the institutional investors who have started to totter along in sidecars with them. In fact, so much Wall Street money tried to jump the IPO gun that the much-feared bubble was nudged into secondary stock markets.

To some extent, the caution that burned public-market investors have applied to tech IPOs in the past decade is now being applied in the private-financing market. That doesn’t mean money has dried up, it’s just become more soberly discerning. As Sarah Lacy put it, “The good companies are digging deep to survive. No one I know is freaking out. Everyone is just getting to work.

Or in other words, everyone is growing up. But the tech sector is showing signs of becoming a mature industry in other ways. Many of the best performing tech stocks were ones in turnaround, companies that faced huge setbacks and poured their energies into righting themselves.

AOL rose 96 percent in 2012, after Tim Armstrong cunningly engineered a plan aimed at pleasing investors if no one else. Netflix’s 34 percent rise outpaced Apple’s 32 percent gain, thanks to talk about a takeover. Similarly, Yahoo’s 23 percent gain was better than Google’s 10 percent, simply because of hopes of a recovery.

This is watchable drama, but it also looks like older industries like manufacturing or retail, where companies being pulled back from the brink are favored over peers who have been doing well all along. That’s more of a value story, not the growth story that has been the narrative of Silicon Valley for the past three decades.

Growing up isn’t necessarily bad for an industry. It means less appetite for me-too startups that ape a business model someone else turned into a success. So LivingSocial is having an even harder time than Groupon. And music sites like the rebranded MySpace face a tougher trek up the steep mountain that Pandora climbed first.

But some developments of 2012 are more troubling. The most disturbing sign of the Web industry’s maturation is that a few big companies are changing the rules in ways that benefit themselves over their customers. Having a few powerful players isn’t necessarily a bad thing in a sector. But Apple, Google, Amazon and others are practicing what I think of as captive consumption – the practice of corralling and trapping users into your products, rather than enticing them with quality and innovation.

And this is where I see some hope for the Web in 2013. The metaphors of childhood and adulthood break down when applied to the business world because truly innovative industries can essentially regenerate their way back into creativity and growth. Silicon Valley has done this several times already (processors –> PCs –> boxed software –> Web). There are areas like mobile apps that are far from exhausting their potential and others like 3D printers or augmented reality that promise some pretty disruptive changes down the road.

Big change isn’t coming on its own in the next year, however, but I believe the Web could regenerate its way new growth. Simply put, this means returning to ideals that designed the Web in its early years: Putting the user on top, honoring the privacy of data in a way that encourages its disclosure, making open a core principle and not a hollow buzzword, and designing your product or service in a way that makes your customers want it, instead of feeling they are trapped inside it.

Simple to say, perhaps, and maybe idealistic – that is, difficult to achieve in that it takes a good deal of will from the companies making money off the web today and the people investing in them. But if something close to this were to somehow happen in 2013, then a year from now we might be saying goodbye to next year in a spirit of giddiness and ecstasy about great things that won’t disappoint us later on.