Ideally all regressions would be bisected, but that's clearly not the case. You can of course argue about terminology and / or mechanism, but I think it's useful to distinguish "possible" regressions from confirmed regressions with a commit id. Personally I think it would be nice if bugzilla could give me a list of commit id's and associated bugs, so I could use git and some scripting to do additional processing on that.
Perhaps the real issue is that the list of regressions is large enough that it becomes somewhat impractical to go through them on a regular basis to look for regressions that aren't bisected yet though. There are currently 338 bugs with the regression keyword, of which 64 have the directx-d3d or directx-ddraw component. I'm currently CC'd on 10 of those, most of which are not so easy to fix for one reason or another. In my personal experience, the majority of regressions aren't necessarily a problem with the original patch, but rather existing problems becoming more visible, etc. Perhaps that's different between different developers and different components though.
It doesn't really matter who's fault a particular regression is though, what it comes down to is that you touched something, and now it's broken. So if I'd be reviewing a wined3d patch from someone, I'd balance the likelihood of that patch / developer breaking something versus how likely it is that that developer is going to fix it in a timely fashion when it does break.