It's never only about the ratings. There are lots of factors that go into the renewal decision, many of which we never hear about. How much confidence the networks have in their new pilots each year plays a big role in cancellation plans. We don't see those new pilots until months after the decision has already been made.
And even then, who knows whether we agree with it? Fox wasn't going to pick up Alcatraz
until JJ Abrams convinced them that he had a great storyline to unfold. He must be an incredible salesman, because I watched the whole season and didn't see anything approaching a great storyline. He should have sold Fox the Golden Gate Bridge while he was at it.
Take the weirdly common notion that foreign ratings "don't count." I'm sure they do, in cases where networks are profiting from those ratings. Why would any business ignore any revenue source? But has anyone seen a good listing of foreign ratings, especially one that comprehensively includes all global markets? I sure can't find one. So it's impossible to guess how much they count.
In this case, Warners and Bad Robot lowered the license fee, and that did the trick. I'm sure the fact that Fringe is warming the Friday night deathslot was a factor. What is Fox going to put in the deathslot instead? And their pilots pickups have been light this year, considering how many shows they've cancelled or are bound to cancel.