Seeing as the first versions of DRI date to the late 90's, I'm not seeing your point. Linux has been supporting that kind of stuff just as long as Windows, give or take a year or so - I remember it being a big deal back then, having proper 3d support for the Matrox card I had back then (state of the art, at the time).
There was also something called "Utah GLX", which I think predated DRI, but I don't really remember much of it besides the name. I do remember that getting hardware acceleration used to be a bit of work, because it relied on some "agpgart" module that wasn't yet part of the mainline Linux kernel. Even when DRI began to work out of the box, it was still a bumpy ride because of rendering glitches, software fallbacks and - at least with my Matrox card - semi-frequent lockups. (The lockups got rarer over time, but they never quite went away.)
These days I have an AMD card, and while that was also quite a bumpy road (partly because I got it while the open drivers were still beta quality), things are so much better now. I can't even remember if I've seen any lockups since the switch to Gallium3D, and for that I'm very grateful.