GSP walks in around 200-210 lbs and fights at friggin' 170 lbs...
Fight time weight for GSP is ~185.
Also, most fights that receive votes for fight of the year (FOTY) generally end in decisions. The "Korean Zombie" vs Leonard Garcia is in the running for FOTY for 2010 and it ended in a split decision.
I was hoping GSP could finish Kos, but I think his best chances for doing that were via sub, and he wasn't able to keep Kos on the ground long enough to mount any offense there. Give credit to Kos' elite-level wrestling for that though, not a GSP deficiency.
In the case of Fedor, and Aldo finishing fights... look at who they have fought. Fedor twice wasn't able to finish Big Nog when they were both in their primes. He didn't finish Cro Cop. Aldo didn't finish Faber, though he had 5 rounds to do it. He destroyed his legs, but didn't finish him. Most of his other stoppages were against mediocre fighters. Of the 3 stoppages Shogun has in the UFC, 2 of them were against washed up fighters (Liddell and Coleman).
GSP is incredibly well rounded. Most fighters that finish fights consistently excel in one area, and are adequate in others. The only area that GSP excels in is wrestling, but that alone won't finish a fight. Plus, the 170 lb division is one of the deepest divisions in MMA, so there are no "easy" opponents (except Dan Hardy). Also, the 170 lb division is chock full of some of the best wrestlers in MMA, so the fact that GSP is at the pinnacle of that division, without having the amateur wrestling pedigree that the majority of his opponents have, says a LOT about his talent.