Actually he wears 3 socks.. He has switched from the old nike cushioned socks circa 2006-09 to the ligher thinner socks, so he uses 3 socks now...
Look very carefully at the top and you will see his base layer sock on the right..
I (somehow) managed to be in the lockers at the same time as rogisexiclass at the Dubai tennis recently, and after taking his socks off, he had a ridiculous amount of tape around his ankles underneath the socks. As in it must have been almost 1cm thick. It was almost like a cast, and when he took it off it actually retained its shape it was that thick.