For the most part, this is minimal syntactic sugar, not significantly different semantics.
> How does CS have more dependencies than any other compiled language?
It does not, the point is that javascript has no dependency, and that if you're going to add a compiler dependency you might as well go for real changes.
Has LLVM grown an assembly frontend? Emscripten is more or less an LLVM backend.
> and Native Client.
These are no more web applications than writing firefox extensions at this point.
> Semantics aren't quite identical (scoping, implicit return values, fat arrow functions).
For the most part, this is minimal syntactic sugar, not significantly different semantics.
> How does CS have more dependencies than any other compiled language?
It does not, the point is that javascript has no dependency, and that if you're going to add a compiler dependency you might as well go for real changes.