First of all, there are more things than typed arrays (vectors) in AS3, the main thing being a consistent runtime. Also the way you structure an AS3 project is different since the language supports packages/classes etc while in JS you (for better or worse) don't have these concepts so you end up with many different code styles. Even though browsers implement the some of the features, there are subtle differences in the implementations. This results, in real world scenarios, that this stuff are being abstracted away, layers and layers of abstractions, libraries for everything. I have my doubts that this SWF interpreter can be efficient.
Sure, but from what you said I'm guessing that they don't work in IE9, which is what I mean about cross-browser issues. Plus, TypedArrays are somewhat clumsy maybe?
It seems as if JS is the future, and that's not necessarily a bad thing, but it would be nice if JS had a few more features to make it easier to use. I personally wouldn't be opposed to starting clean (with something like Dart) but that's probably unrealistic.
Overall, the reduction of plugins is a good thing, who doesn't like less security holes, less software to update, etc. But it's also a bad thing if we lost features off stuff, lose functionality, loss cross-browser capabilities etc.
Also, can't believe I said "righting" instead of "writing" in my last post. That's quite cringe-inducing.