I'm not 100% sure, but my experience has been that scripting languages are more compact in terms of code:
http://shootout.alioth.debian.org/u32/benchmark.php?test=all...
In terms of the API, well, that depends entirely on the project and their goals! A small, decent team of open source developers could probably cover most of the API in less than a year without particularly working that hard on it.
The real problem here is that interpreters for the iPhone seem to be a gray area at best (see discussion elsewhere here).
Anyway, looks like good work, and I think interpreters on phones are a great idea:-)