Just mirroring what devs already do.
CSS3 colours have been in common use for years now, even thought CSS3 is still under development - any transparency on a website other than from GIF/PNG is thanks to this. Likewise border-radius for round borders, CSS3 transform (think google maps and openstreetmap), Server-Sent events (gaining traction for webapps), gradients video and other fun stuff.
All of these can be applied now, across browsers, without too much difficulty (I'm not too familiar with IE but I believe IE9 is not too bad, astonishingly). There is a steering commitee of sorts and the architects of the various browsers collaberate: things are not like the bad old days, this stuff is documented and tested so there's no need to guess and the vast majority of browser hacks are no longer necessary - usually it's just a matter of browser-dependent CSS prefixes, becuase the official spec is unfinalized.
Meanwhile the W3C, with the same goals and even mostly the same people, only managed to ratify CSS2.1 last June. It's prototype-led development vs. mythical-man-month style formal specification. Without the WHATWG we'd have to rely on just the latter and that, IMHO, would be a disaster.