There's an obvious counter to that argument, in the fact that BJ couldn't do anything with Georges inside his guard.
I love BJ, I really do. But the only dramatic improvements in his game (since losing to Hughes) have come in the form of better conditioning, and probably crisper boxing. He's always been a dangerous striker, and he's always been a phenomenal grappler, especially when he's on top. Once again, he's never been anywhere near as dangerous off his back in MMA as he is when he is on top.
Give me a break, BJ trains for every fight. He was simply outwrestled and controlled for rounds 2 and 3, by a much larger and naturally athletic opponent.
No one is saying he's the "Nogueira of MMA BJJ", way to blow it out of proportion. GSP has been able to outgrapple every single person he has faced in the octagon, except for Matt Hughes---a loss he avenged through drastic improvement in his ground game---and BJ, who also couldn't do anything with GSP on the ground.
Where has BJ improved? BJ is more or less the same fighter GSP fought the first time, with better boxing technique and better cardio (at 155, who knows at 170?). His ground game is great, as always (from the top position) but he's never been known for pulling-off subs from his back. I definitely think GSP has grown more since the two fighters last met, although they're both very complete fighters in their own rights.