I gotta laugh at the "real tennis fan" argument being made here. While there's no doubt that some people will only watch for player X,Y,Z and don't care for the sport in general, I think it's hypocritical to criticize depressed Federer fans. Fact is, everyone, including the "real fans" who watches the sport will develop a fondness for player X,Y,Z over time. Back to Federer, it's only natural that his fans are disappointed by his absence from the tour this year, however that doesn't necessarily make one a lesser fan of the sport. Watching tennis matches is time consuming, we all have a schedule and things to do, so if your favorite player isn't playing, then perhaps you won't invest the 2-3 hours to watch a tennis match on TV, or the couple hundreds of $$ to attend a tournament because the incentive/excitement is gone.
I'm a proud Fed fan, who started to watch in the Sampras era. For me this kinda feels like "déjà vu" even though Roger is an even bigger star than Sampras. They're will be a transition period after Roger hangs the Wilson wand. It may last a couple of years like when Sampras retired, or it might last more than a decade like in the WTA, but eventually someone rises. Will that someone transcend the sport and become an icon like Federer/Nadal? Maybe, maybe not. Until then, does that mean I will stop watching tennis or even playing because Roger is gone? Not at all. Will I invest as much time watching tournaments or even traveling around the globe to watch tennis tournaments? Probably not. I'll still watch, but I won't go out of my way to do so. Does that make me a lesser fan of the sport? I don't think so.