Blake is a good Challenger level player now who can occasionally rise and make a good run at an ATP tournament. He can still compete at Tour level though. At one point he had won 9/10 first-round Tour-level matches on the year, I think.
There'll be a whole bunch of players retiring at the end of 2012. These 2 are among that group.
Why would Ivo retire exactly? I contend that his backhand is as good now as it has ever been, and if he keeps hitting it down the line like he did earlier in the year he can absolutely cause problems for people for the next couple of years.
We should be appreciative of Federer though, because we will never see anything like him again. The fact he can still compete for slams ever after the erosion of his physical skills is really a greater testament to the natural talent he has than the period of time when he was dominating the tour.