Regarding Javascript: there are at least two or three mature Java implementations out there, and many more non-Java ones. Its inconsistencies and most implementation gotchas are well-known by now. Also, it's a comparatively simple language that has not experienced as much organic growth as Python, Perl, or Ruby.

I am still impressed that it can beat V8 handily without extensive further optimization work in the JVM, but it's not that surprising.