I'm going to be blunt.
Done right, there's NOT the variance people keep bandying about on the subject. The rub's in doing it "right" just like knowing there's a right and a wrong way to going about producing production installs under Windows and MacOS- and if you're unfamiliar with it, it'd seem like an impossibility (I'm sorry, there's as much variances in the forms of device driver issues, coupled with Windows versions (Let's see... XP, Vista, Windows 7...) as there are realistic variances within Linux- and you don't get that one as an out...) when, in fact, it's not.
Then don't forget to write a mail.
http://www.valvesoftware.com/jobs/index.html
I didn't mean that it would be difficult to port the games so that they run on different distributions, but rather that it would be difficult to provide support for users when they have problems. Just take a look at the Ubuntu forums and the number of users having audio problems with games. It isn't usually something the game developer has done wrong, but rather there's an issue with the driver for their particular hardware or a problem with pulse audio etc. If steam provided a Linux client they'd probably have a lot of Linux users with issues wanting support.
As Svartalf said above: The rub's in doing it "right".
I've seen a lot of "hacks" in games even on Windows in a way that you would like to commit suicide if you had build that crap of code. So it's incorrect to call all the blame on Linux failing at sound. The fail equation contains a lot of variables and Linux is just one of them as is hackish code.
There's also forums for Windows, filled with problems they are having with their operating system...
I'm guessing, just as a user not a developer, that a lot of the problems with third party software on Linux, games in particular comes from not giving half as much time to spit and polish as on the Mac and Windows side.
I guess we could say that the lack of standards for Drivers or Distrib causes those issue like Pulse audio cause sounds issues in any distrib. For instance, I use mandriva and i've got pulse audio disabled (i really hate this sound server), for some ppl it works fine but for other (me included) have tons of issues (sound glitches for VOIP). For a game Dev the best way to go is to have a standard API like OpenAL, like that the blame won't go to the game but to the sound server being used. Anyway that's how i feel about this problem.
You can compile openal against pulse audio too btw. Often you can remove the shipped depends often and use system wide installed ones. In some cases you need symlinks - especially when non standard names have been used for the libs.
That really depends on how up to date your PA install is.
PA is working to wrap up all former audio packages into a single meta server. It is closest thing we've ever ad to a unified sound system.