im british but people who say the uk are wrong. in my opinion, compared to road racing track is a lot lower standard and the reason britain are successful in it is because they focus on it a lot more than many other nations. i think bradley wiggins is a perfect example of this, he won the olympics but in the tour prologue over a similiar distance he finished 16th (or maybe 17th..), he was beaten by a lot of riders who dont race track, if people like george hincapie and thor hushovd chose to focus on the olympic pursuit then i am sure they would beat bradley wiggins. compare the calibre of riders racing track and then look at road racing and youll see what i mean. basically i think that the standard of track racing is nowhere near that of pro road racing.
also how can you definitively say which nation breeds the best cyclists? belgium produces many strong one day classics riders whilst a country like spain produces a lot of climbers and tour riders. you cant say that tour riders are better than classics riders or vice versa, so you cant compare nations because they often produce extremely different types of rider due to the nature of their domestic racing setup. tom boonen or phillipe gilbert arent going to win a major stage race anytime soon but then carlos sastre is never going to win flanders...