Not true. In order for Flash to support anything, the browser first has to support it in the plugin framework. This support varies by browser and by browser version. There is a chart on some Adobe employee blog somewhere.
http://www.kaourantin.net/2010/02/core-animation.html
Again two different modes of operating. Flash goes out of its way to maintain backwards compatibility. Not only this aspect of operating with a long list of browsers, but there are two virtual machines shipped: Actionscript Virtual Machine 1, AVM1, (Flash 8 and earlier ) and AVM2 ( Flash 9 and later ).
Apple on the other hand won't even backport this new low level API to Leopard (10.5 ) .
Somewhere between the two extremes would be a more reasonable compromise. There is some really old Flash code that probably should die. And Apple is just being lazy and snide. (they know that will still be plenty of folks bitching about Flash because have limited the GPUs this will works on; the vast majority of deployed Macs do not have them. )