Those are all HTML5 features, right? We've gotten into this weird place where the standards are being implemented while they are still in flux because the browser makers are just anxious to add new features.
We've always been in that place. As Mark Pilgrim put it: "Most of the successful versions of HTML have been “retro-specs,” catching up to the world while simultaneously trying to nudge it in the right direction." -- http://diveintomark.org/archives/2009/11/02/why-do-we-have-a...
Microsoft themselves added HTML5 features to IE8, and have more planned for IE9 so saying they're HTML5 isn't in itself a valid reason not to bother implementing them.
Some people believe that independent implementations of standards can uncover areas that are unclear or impossible and make the standard much better from the experience gained. Microsoft are notable in complaining about this in standards that threaten their profits while at the same time just doing their own thing in code and later trying to get it standardised, warts'n'all. It is more than a little hypocritical.
How many different version of CSS Gradients are out there now? It seems like they still just roll their own, but now they do it in an "accepted way" by using a prefix like "webkit" or "moz" on their new stuff. It doesn't do much good for the implementers though.
As you can see CSS3 is very far from being "finalized" so any implementation that mozilla or webkit or someone does is just their best guess at what the final standard will be or experiments to provide recommendation. They leave the prefix free version for when they actually know what it is they are implementing to cause less pain in the long term allowing developers to know full well that what they are using is far from finished.
