It could always be the hardware support mind.
As I've had no issues with UT3, Gears, Bioshock or CoD4 on Vista in either DirectX9 or DirectX10.
I found that Gears and UT3 until patched would crash trying to play multiplayer though; which annoyed me a little especially Gears as I had to manually download the GFW - Live updates as the game would crash before it completed downloading and updating.
Although more and more now, I have started getting games that normally I would've bought for Windows (as it's cheaper) spending a little more and getting the 360 versions. Simply because it's guarenteed to work, no issues because of DirectX or the version of Windows you're using, some background application, etc, etc...
It's nice to put in a disc and know in a few seconds you'll be playing rather than getting home with it excited then getting bored waiting up to 35minutes for it to install (no joke, Gears of War took almost 45minutes to install!!)
I find it amusing people are going "yay" over Installs for the PS3 and Xbox 360 because it will "enhance loading times"; but personally I wish to god we had the option on the PC to just run something from disc. I could put up with extra loading times tbh if I didn't have to spend so long installing the damn thing then defragging to enhance performance because the HDD fragments over time due to useage.
I mean the installation argument would be valid if you didn't still have to insert the disc. Only way around that is using a Virtal Drive which means you use up Install Space + Disc Size as the total disc used. In the case of Gears of War that means you are using close to 18GB for that one game. Which is a point they said that they cut the extra content from the 360 version cause of space restrictions... yet for the PC it fits on a 9.2GB disc (installs at just under 9GB)
I don't see how it wouldn't have fit tbh.. not as if it's even that bloody much extra.
Consoles aren't slowly killing PC gaming, the PC's very nature is.
Constant upgrading with no "standard" performance marks for developers meaning you can't simply buy mid-range anymore... instead developers are looking at the PC market as a "test bed" or a bit of additional income with piss-poor ports hoping the additional performance available will make up for it.
The over useage of Unreal 3 also isn't helping as the engine still isn't quite ready for PC primetime imo; especially with epic now focusing almost solely on Consoles despite knowing that PC developers will still use their engine.