Is there a reason why people work at like 5-10 reps/set on every muscle except abs, where they'll do like 50 or even 100+? Same goes for frequency -- a lot of people hit each muscle once a week but will do abs nearly every day. It's not a rhetorical question, I'm seriously asking.
I've switched over to adding resistance to keep it in the 10-15 rep range, thinking hey, if I want my arms to grow I need to lift heavy, so what's the difference with the abs? I can understand working abs a little more frequently though, as I've read that they recover faster than other muscle groups.