if weaver was strictly a fastball pitcher that had relied on overpowering hitters, i'd be greatly concerned.
however, since his strength is control and deception, i don't have any concerns about whatever the radar gun says. what he's doing works, and ultimately that's all that really matters. lots of different ways to skin a cat.
and don't forget, guys like tommy john, jamie moyer, john tudor, and some others still had success throwing in the 70 mph range. speed isn't everything.