Should have been Heavyweights! I mean, there are SO many good reasons and opportunities.
1) Brock and JDS are both heavyweights. Sure, techniques transcend weight classes but they would be best suited to train and spar with HWs. I'd argue some techniques and training methods that are used at lighter weights aren't always viable for heavyweights and vice versa. Except for maybe the shooting star press :). Anyone can do that.
2) 2011 is being touted as the year of the heavyweight. Why not play right into that meme?
3) SF is doing HWs bigtime. UFC should fight in that arena as well. UFC's roster of HWs isn't that strong, after the top bracket. They should be working hard to recruit some quality new HWs and TUF is the place to do it.
4) Just imagine the impact of 14 or 16 heavyweights and Brock and JDS on the show. It would be MASSIVE (in more ways than one).
5) Don't we have enough quality WWs already? It's a shark tank there. Especially with Diego and BJ just recently moving into WW and doing well (therefore likely to stay). And you've got all these quality fighters waiting for title shots - Fitch, Sotiropoulos, etc.