I don't think it's about sexiness -- Python has brought many associations to mind over the years, but sexy has never been one of them -- just that there are only so many languages that can compete in the same ecological feeding space that (Python,Perl,Ruby,Groovy) are all pretty much butting heads against each other over.

If anything, Python seems to be dominating in large part because of its unabashed lack of sexiness (or what passes for it in modern programming circles: cleverness, and cuteness).