Yeah, I noticed that as well... Kind of bizarre. Especially since Rhino was a pretty good educated guess; I went and took a look at it as well since I know there are some pretty performant languages running on the JVM that aren't Java.
For whatever it's worth, I think the problem Javascript is going to have with speed is that it is so dynamic that it makes it difficult for compilers to optimize. If it ever got type hints it would probably be much easier to make fast.
