Nationalism? The whole idea of it is to be competetive and for fans to get their nation/team/pairs/individual. They aren't just jogging around the track to show off a few different coloured vests.
I mean c'mon... I even supported a Welsh girl in the TKD and a Scot in the cycling! 
Wilkie - Winning does mean something. i.e the 800m. They all set about the task of being able to complete 2 laps of the track faster than everyone else... the person who did it fastest proved he had prepared for and carried out his race better. That will mean a hell of a lot! Are you telling me if you won a gold at the olympics and took a WR making you the fastest person ever to officially complete that distance you wouldn't feel anything? honestly?
I, personally, would probably feel very chuffed, if I won something. I wouldn't expect it to mean much to anyone else though.
If a friend won, I'd be very happy for them.
I don't care about a bunch of strangers whom I will never know. Whether the person who wins in English, German, or any other nationality is neither here nor there. An English person winning doesn't mean all English people are suddenly somehow better.
So they are the fastest, can jump highest/furthest, makes them good at their sport, but that has no impact at all on anything else (except, as KK points out, their earning potential).