^ Yeah, clearly he's well known because of all the Wimbledon titles. A lot of brits only watch Wimbledon, and a large chunk will only be interested in tennis enough to watch the final.
It's not just the winning though - Sampras won as many Wimbledon titles and didn't have that sort of following. Federer almost seems British so that might have something to do with it.
Underdogs who put up a good fight are also roundly appreciated not just the winners.