No I know, but my point was it's not necessarily hard to put Silva on his back but once you get him there you have to worry about subs. And GSP has been subbed before. So it's not like it's a done deal if GSP were to get him down and using the Lutter/Hendo/Sonnen fights to illustrate how GSP could win is terrible since ALL 3 of those guys were subbed on the ground.
The biggest problem like people have mentioned is the size difference. GSP could add weight, but then the attributes you listed (athletic and explosive) would be sacrificed somewhat. Look at Mir, packing on muscle/extra weight did nothing for him against Lesnar and Carwin.
Adding weight could actually negatively impact GSP's game in a fight against Silva who's naturally a bigger guy.