I feel I should point out something no one seems yet to have hit upon.
Flash is a bytecode format. You're technically not restricted to using ActionShit at all; if someone cared enough they could make an SWF compiler for (e.g.) Scheme.
I think the other dubious advantages and disadvantages of either Flash or that disorganized mess of Javascript+HTML+SVG+Canvas+whatever else pale in comparison to the flexibility of having a bytecode format into which all manner of languages can be compiled.