djokovic started winning back in 2008 when both federer and nadal were in their primes. he beat both of them on their "home soil", had some record breaking seasons. he's also incredibly consistent, he hasn't been out of the top3 for ages. and yes, most new number ones usually overtake aging rivals, that's no surprise in sport.
the "he's winning because of the lack of strong rivals" argument is pretty weak. who did federer had as strong rival? 30+ year old agassi or that poor roddick? who did nadal had? that federer who only came to rule the tennis world because of the lack of rivals?
