But I wouldn't even say that. Look at the C/C++ situation. Microsoft as a platform doesn't support a ton of C, every compiler has it's own ways of using undefined behavior, there are tons of extensions and "only works on compiler X". Look at python where even if you ignore the 2/3 split, you have ironpython, cpython, pypy, and more that all have their own quirks, differences, and incompatibilities. It's pretty often you see a python library that only works on cpython.

For all it's issues, JS has mostly moved past that. It's pretty rare to see a javascript program or library (that's not just a tech demo) that only works on one implementation. Hell Microsoft released a node.js fork that runs on chakra, and to my surprise every single one of our node applications runs on it without a single change or hitch. (i haven't looked up if this is "normal" or if i got lucky though, so take it with a grain of salt).

Now obviously it's not perfect, and we should strive to be better, to fix these issues, but it's not like javascript is in some unprecedented scenario here. I actually think that the IE6 days have pushed JS to fix a lot of the problems that are plaguing other languages in this area.