It's never too late to do the right thing. As an extreme example, everyone who's used to it now, will eventually die, and I'd venture to say the web will outlive them all. (although probably not in its current form, but that's kind of the point) CSS3's solution is a good one because it allows people that are used to it to keep using their old dodgy hacks, and it also allows people who prefer logical consistency to opt in to that. It's definitely not too late.
True, but there's a continuity of already-written code and learning, both from those alive now and from that already-written code, that keeps things that aren't sufficiently bothersome from getting changed.
And this "extreme example" somehow proves your point that it's "never too late"? If it includes people having put it with this dying, then I think, it IS too late.