Its the smart move right now.
There is no one else at 185 for him to face. He destroyed Rich 2x, and Rich has destroyed everyone else... what does that tell you.
I guess he could stay at 185 and fight Bisping, but realistically thats a 1 round fight for Silva.
The 205 division is stacked... Griffin, Liddell, Rampage, Wandy, Henderson (he will fight at 205) etc... Its a good division. He has some potential big bouts in the division. Headliners that will pay him some serious jack!
He will be undersized at 205... Griffin is 230 when training, Rampage last week he was up around 240-250 this year, I highly doubt that Silva walks around at anything more than 205...maybe 210.
He needs to add some serious muscle ... but the guy is well rounded, excellent power and stricking, a great ground game...
I think he will do well against the Jardines and Irvins of the 205 division, but the "A" fighters will have a huge size advantage, will have the same power (if not more) and will just be stronger. But only time will tell...