Cant see how AS3 itself improves Flash games. Just because it follows ECMAScript standard or is OOP doesnt make games any better. I actually see leap from AS1 to AS2 bigger then AS2-AS3. Pretty much everything you can do with AS3 can also be done in AS2. I also have not yet seen any significant speed increase in AVM2, the perfomance in drawing the graphics is same as before and while the code executions may be faster there are very few games running so much code that it slows down the game.

The main problem with making AS3 complex and "mature" as every other programming language is that when someone is able to write AS3 code he can write same code in any other programming language too. And if he can program in other language why would he choose to use Flash? The AS1 was much easier then other programming languages allowing people with no previous programming experience to write games. AS3 is not something you pick up in days and when you need to decide to spend next couple of years learning AS3 or some other programming language there isnt many good reasons to go with AS3.