I've hung 3 tv's, a 52, 60, and 70 using molly bolts directly into the steel studs. I'm paranoid about anchoring directly to drywall. The 70 is only on 2 studs with 4 bolts just given how I wanted the TV centered and where the studs were located and it's been fine.
I can't find them on the Home Depot website, but I've purchased them both from the HD in the NE and the one by Chinook.
http://en.wikipedia.org/wiki/Molly_(fastener)