If you notice how easy GSP was able to pass BJ's guard, as well as his rubber guard.
Well, he made it look easy, true.
Penn's guard is notoriously difficult to pass, and either GSP is just THAT GOOD, or the the grease from his back transferred to the back of BJ's calves, and BJ coudn't get the proper friction to hold him down.
I dunno... in no gi grappling grappling (with t-shirts, nevermind topless) friction doesn't play nearly as big a roll in my experience, especially after the first couple minutes. In fact one thing I found in the switch from gi to no gi (with shirts) was instead of thinking in handles, you had to think in hooks for just that reason.
That said, when I saw the fight, and gifs of GSP passing, I saw some food for thought:
He always had a overhook or two around the back of BJ's neck when in his guard.
Whenever BJ tried to hook a shoulder with a leg, he would immediately move his shoulder out of range by hauling in the neck, like a plum, but horizantal. Normally when people try to hall themselves out of guard they get swept because they give up the base, but in this case with one leg up already, BJ gave up the sweep. he picked his moment well. Then he'd punish BJ as he tried to recover position.
To me that looked like good technique with good sensitivity and a fatiguing BJ. Now if BJ had landed the hook and then it miraculously slid off, okay, I'd be like "grease?", but the hook never caught.
When he escaped the rubber guard, well, the neck is pretty the weak compared to the arms. For example, one bearhug escape that's served me well against wrestlers up to a certain hit involves pushing against the head. Most newbies get armbarred doing it, but most newbies don't know what to look out for. The rubber escapes I saw all had GSP pushing off the head. Kind of reminded me of this GJJ escape from a headlock I learned once.
Now, if gsp's head just slipped out as soon as he pulled up, again, okay, grease may be the word. But I saw mechanical force behind the movement, not slipping.
Now, I dunno if these are the same things you saw, maybe we're talking about different moments in the fight, but I'd say GSP had taken on a series of counters and counter strategies tailor made for BJ's arsenal in an MMA context.
OTOH I've never been in the octagon, so my opinion is just that at, the end of the day.
And the idea about burning out the shoulders... sheer genius. Bit of a gamesman, that GSP.