TV Squad posted a great analysis of why NBC picked up 30 Rock for a second season, but has held out on Studio 60.  From the article:

…it can’t be because 30 Rock got better ratings than Studio 60, because Studio 60 got better ratings. It can’t be because 30 Rock got a higher rating in the all-important 18 to 49 demo, because Studio 60 had higher ratings there, too.

Read the full article here.