The last American before Nicky to win was Kenny Jr. He only won because everyone else hit a bad patch, much like Criville the year before winning because Doohan crashed and retired. In 2000 when Kenny won, on a PoS Suzuki, it was because Rossi had just joined and was in his crashing year (125s, crash a lot, win the next year. 250s, crash a lot, win the next year. 500s, crash a lot, win the next year.) but, like Nicky, where is he now?
A seriously talented racer wins several years in succession, on different machinery. The other racers have to hope Rossi has an off year to win.
Hmm... that's an interesting statistic. Every year Rossi has been in the top class, the years he's not won have been won by Americans.