The thing is -- it wasn't only top control that won the fight for GSP like in the OP. Control is one of the less important criteria, but still scores points.
However to get top control you have to get takedowns, which GSP scored at least one in each round (7 total), which count towards effective grappling... which is an important criteria. Sort of a little domino effect -- to get (top) control, you need a takedown, which gets you points in a number of areas.
He also scored a lot of passes once he got the fight to the ground, which further helped his grappling and control. Finally, he landed more significant strikes throughout the fight as well.
I think I've beat this to death tonight - time to call it quits.