People over estimate the advantage weight gives.
I'm not saying weight classes are a bad thing.
When it comes down to the top 3 fighters in the world (jones - silva - gsp), the winner of the fight isnt going to be because of a weight advantage (bar gsp-jones obviously). We've seen Bj penn beat up ww's, frankie edgar beat up lw's, silva beat up lhw's, cain beat up lesnar, kosh beat up johnson, vitor beat up johnson (haha sorry johnson), vitor give jones the fight of his life, hendo knock out fedor... There are SO many more.
More than not, the winner of the fight comes down to who was the better man on fight night. OF COURSE exceptions do exist, but more than not skill is going to beat a weight advantage unless its just insane.
A catch weight is proper simply because of how much silva would have to drain himself to make 170, and at 178 all we are really talking about is gsp cutting a few less and anderson cutting a few more. It's completely fair.
I think GSP is really just scared of getting less endorsements and payed less by sponsors. Right now, the speculation of who is #1 is what makes these fighters get so many deals. I can ensure you the winner of this fight would have millions of dollars waiting for them on Sunday from sponsors and people wanting to endorse the "Undisputed best fighter in the world".
What GSP might not realize though is the amount of money he would get payed by the UFC, Sponsors, and Endorsers for this fight would probably equal out, if not be more than, the amount of money he would be making even if he lost.
Before one says "Silva can fight Jones!!!!", Yes, he absolutely can and jones/silva both said they would fight each other if they had to.
Right now, Uncle Dana wants GSP/Silva. When Jones beat Belfort he wanted Jones/Silva. Uncle Dana doesn't know what he wants, all he knows is he wants silva in a super fight and because silva WANTS gsp, hes trying to make it happen seemingly because he won't have to pay silva/gsp as much to fight as he would silva/jones. That and he knows Jones is fairly young and could do a super fight at heavyweight one day AND that jones plans to. There's simply alot more money in making GSP-Silva happen then Jones-Silva because GSP isn't going to test the waters in a different division because he is too scared to lose.
That's what makes Silva so unique. He's fine with fighting fighters from other divisions, he does want to test himself, he's not scared that he might lose. Jones WANTS to also, but he obviously wants to have a real camp to make sure he doesn't lose.
And dang, just thought of condit @ 185. Lots of interesting fights for him there... though he wouldnt have anything for silva, he could easily be top 5 i think.
There is a flip side to this. Anderson agrees to 170. Crazy...
I could see this happening, but I sure Silva would still want it to be a non title fight, which would destroy the WW division if he did win. Silva stated plenty of time he wants to end his career at 185 and i really don't see him wanting another title. Which really raises questions on what would happen if Silva-Jones fought.. I think Silva wouldn't mind fighting @ 205, its just that nog and machida fight there and because of that its probably not even an nor desire for him to be a champion of a division that a mentor plus a training partner/good friend fight in.