1) Brock's nuthuggers very quickly shut the fuck up about Brock being able to take Fedor on major MMA forums like Sherdog. After watching Carwin (who is not known for his technically sound standup) knock him on his ass and then beat his face in for three minutes, they realized Fedor was better than Lesnar in every aspect of the game, that his size does not make him invulnerable and that he would likely get "Zulu'd" by Fedor's far superior standup.
2) Now that Carwin has tried, the only real contender left in the division that's currently signed to the UFC is Cain Velasquez, who I don't think has the size or skills to beat Lesnar. He's a smaller version of Lesnar in the same way that Carwin was a bigger version -- similar wrestling credentials, a little BJJ and not much else. His 8-0 record is padded with about 6 wins over nobodies, a win over an aged and pretty much "finished" Nog and an overrated Kongo.
It won't take long for White to notice he can't keep spouting his "hurr durr our HW division is the best in the world" when it's filled with guys that are large, one-dimensional wrestlers with mediocre standup and little to no submission game. This opens the way for White to sign guys like Josh Barnett, Aleks and Fedor Emelianenko, Mark Hunt, Overeem, Werdum, etc.
The Top 10 Heavyweight Rankings right now are a joke. Junior Dos Santos, Frank Mir, Brett Rogers, (and as much as I hate to say it, Nog) etc. have no place in the top 10 and are only there because better fighters are fighting in smaller promotions and have gone relatively unheard of as a result. Barnett just beat Mighty Mo a few months back and isn't even ranked Top 10, but the winner of fucking Roy Nelson vs. Junior Dos Santos is going to be number 1 contender? Brett Rogers is ranked 10th? Haha. Please.