Check out my HDR comparison thread here: Comparison of HDR Versions (PS3, 360, DC, CPS2)
Basically, the main reason we don’t use HDR classic is also the main reason we stopped using Capcom Classics Collection 2: additional input lag compared to the arcade version. And the reason we don’t use the DC version anymore (which preceded and served as the basis for HDR) is because with it not being used for MVC2 nowadays, there’s not much point in bringing a DC with the rare game (or alternative) and converters to have a great port when it’s not much more hassle to bring a supergun setup to have perfection.
I agree that it’d be splendid to have a ubiquitous modern-day setup but unfortunately, nothing else at the moment is accurate enough compared to the arcade original. To be accepted, a port should have accurate graphics, accurate sound, close speed, unnoticeable lag, and no additional glitches. Competitive fighting game players are normally lenient with graphics and sound to a degree but any major mechanical issues will sink the port. We’ll see soon if 3SOE can meet those standards.
Perhaps on SF2’s next anniversary, a new, faithful port of ST will be released worldwide so that everyone can play on the exact version used and nobody will have to bring CPS2 setups anymore. That’s certainly the hope of most ST players who wish to grow the scene.