Well said, Jim.
To elaborate, Vai brings us the 7-string Ibanez. It puts 7's on the register. Along comes Korn, and they really help propel the 7 into mainstream awareness. The inevitable copying/influenced by/ripoff, whatever you call it, comes along, and everyone wants to sound like Korn, or some derivitave thereof. But they only go with the heaviness of Korn, and overlook alot of the more funky, melodic things they did using the treble strings. So, for Korn, a 7 made sense. They needed range. But to everyone else who just sort of rode the 'Nu-Metal' bandwagon Korn (probably inadvertently) started, they just wanted to go lower. Hence, a baritone.
Jim's ideas make a lot of sense, esp. in this context.
I agree. 7's will be around for awhile. But I think I'm only 1 of a handful of 7 string players here in Toledo. Maybe the only one, actually playing out.