Microsoft's javascript support is just like the other's; slower before but not so much now.
Self fulfilling prophecies? Well, maybe, or maybe it's just an obvious requirement for modern sites. Your list of uses is hardly exhaustive; stack exchange sites use it to great effect; you can't be serious when you prefer hitting f5 to provoke an update rather than...doing nothing and having the site update by itself? Look at google maps today (on the desktop). The limits to the practicality of javascript is...well, there are no limits. It's a programming language; you can do whatever you want with it. Emulate operating systems, games....
http://js1k.com/
There's nothing sloppy about the use of javascript. I think you're a bit of an edge case; perhaps you're better off not using the internet; it really is as fundamental as that.