According to rubygems.org stats page[1], there are 39411 gems available. I think the number 2560 on "all gems" page[2] is the number of gems starting with letter "a".
Ironically, this is the same issue of sloppy testing, just at another level (i.e. missing usability tests on the http://rubygems.org/gems website for at least months, maybe years)
I misunderstood the 39411 number to be the total number of gems submitted over all time, rather than the total number of extant versions. My bad.