Ummm...yeah, first off, Steam isn't available for Linux yet.
The external beta is due to be released in the next few days (by the end of October, barring complications): http://blogs.valvesoftware.com/linux/beta-late-than-never-3/ This makes the above claim true but less-than-relevant. It's true that the first games to be ported will be Source games--particularly L4D games; but Valve has made it clear that they're currently more interested in producing games for Linux than for Windows 8, which Gabe Newell calls a "disaster." This bodes well for commercial Linux gaming. (Also, a lot of folks agree with him regarding Windows 8, so that's also a good sign for Linux.)
Even if it was, the most that's going to be available for a _very_ long time is a few of Valve's Half Life 2 engine-based titles (Left 4 Dead, more than likely Portal 2, etc.), it's not as if every Steam title is going to be magically ported over to Linux overnight. I doubt Valve will even be able to convince one large company like EA to even consider it, so there go everything but your "quirky" indy games like Slender, which was appalling, and the occasional gem.
Several commercial EA games are now available in the Ubuntu Software Center. More are on the way. Some of them are quite a bit more "produced" than an "indie" game would be.
Incidentally, Ryan "Icculus" Gordon? Yeah, he was the one that was supposed to be porting Unreal Tournament 3 over to Linux. In fact I'm sure if you e-mail him he'll still claim that he's working on it. Icculus has a whole bunch of abandoned ports under his belt, people only seem to remember the ones he actually finished.
I share your frustration regarding UT3, as I bought it so I could play it on Linux. Still, Gordon did port a number of other games I enjoy, so I still consider it a "win" of sorts. I read that UT3 had some kind of legal fiasco going on, but that could just be rumor. Anyway, as one of the few folks who have ported any "AAA" games, at all to linux, Gordon is doing pretty well IMHO.
Epic has given up on Linux, iD has given up on Linux, none of the other big companies were ever interested in it in the first place.
The only recent game ID didn't release for Linux, so far as I can recall, is Rage. Quake 4, RTCW, Wolfenstein:ET, Doom 3 (and expansion), Prey, etc. are all available with Linux clients. Id hasn't produced a lot of games, lately, so as you might imagine, these aren't particularly recent titles. I'm bummed about not having Rage on Linux, but them's the breaks. Now that a first-class software distribution platform is coming to Linux, we have reason to be hopeful for future offers.
I use Fedora 17 on my desktop, I've been using Linux since the only alternative I had was DOS 5 or Windows 3.0 on top of it, and even I can see that it's nowhere what it needs to be in order to be a viable gaming platform. That's why I and many others install it -in addition- to the operating system on the PC. One for entertainment (usually Windows), one for everything else (usually Linux). Why? Well, technically you can bash a nail into something with a wrench, but most people would use a hammer.
I tried Fedora for Linux gaming, and it was atrocious. I hassled with it for about 6 months, and eventually went back to Linux Mint. (In point of fact, I had better luck with gaming on Gentoo and Slackware, back when I was using them.) While I respect anyone's preference for a distribution, the present fact is that if you want "mainstream" software to run on Linux, you need a Debian/Ubuntu derivative.
Your comment about dual-booting with Windows for entertainment is certainly well-received, though; until gaming becomes truly "mainstream" on Linux, I doubt I'll be reformatting my Windows partition anytime soon. Likewise, being unable to play some of the games I own is a bummer, so your note about that is also right-on. I hope recent and near-future developments change this.