It has been said by the commentators several times that Kohlschreiber returns serve with the same side of the racquet. His grip on forehand and backhand is nearly the same. I do a very similar thing. In that video though he switches sides. A semi-western/western forehand grip is very similar to an extreme backhand grip and doesn't need much, if any, changing.
Those Federer photos illustrate that he probably has a preferred method of gripping the racquet. The way the overgrip layers over itself creates ridges. If he has his pointer finger laying over one of the ridges and he were to switch sides randomly his grip on the racquet would move slightly up or down with the ridges. I hit nearly all my forehands on one side of the racquet because the ridge is exactly where I want it. If I switch to the other side my grip is slightly too far up or slightly too far down. Even twirling the racquet you automatically stop and get it on the correct side.
Prince Precision 730 - Genesis Twisted Razor 55lbs