Benefits of AS3 over other programming languages

nambo1,

First of all, the real hero is the Flash Player. The Flash Player, the features it has, and the environments it runs in and how it runs in those environments (particularly the web browser, but as kglad pointed, it's very flexible and is used other places as well) is what makes it so popular. ActionScript is simply how you programatically use the Flash Player. ActionScript is an ECMAScript language of which there are others, but it's the Flash Player (and what you can do with it) that attracts people.

The Flash Player has been popular for awhile now. AS3, however, is the latest and completely redone language for the Flash Player. Because it's new and because there are significant differences between AS3 and its predecessor (AS1 and AS2), there is some adoption time required. Many people are still using AS2. You can google to find out a lot more detail about the advantages/disadvantages to AS3 vs AS2, if that's what you're really looking for.

flash is popular because it's (for all practical purposes) browser independent, has extraordinary penetration and flexibility.

I don't think anyone does something in Flash because it has AS3, they do it in Flash because of what you're able to do with it. To do that you would end up using Acriptscript.