I think that's because Disney puffs them up so badly. They give these guys unreasonable images that they can't sustain as they grow older and out of the roles (Miley Cyrus anyone?) and promote them as The Next Big Thing. Then when they wash out or do something against their Image or try to make it in the Big Times...problems happen (Shia LaBouf? Lindsay Lohan?).

Nick stars, from what I've seen anyhow, might not become as big as Zac Efron or Ashley Tisdale, but I think Nick gives them a more realistic experience and expectation set so they can move into the big times (look at Keenan Thompson, he's now on SNL!) and have a solid grounding.

That might just be me though.