ActionScript 3.0 is the culmination of years of development. As each version of Flash came out, developers pushed it to the limit. The next version took into account what developers were using Flash for, and what the weaknesses of the current version of ActionScript were.
Now we have an excellent development environment for 2D game development. You’ll find that one of its main strengths is being able to get games up and running with only a small amount of code.