Motorsport's history is littered with rise and falls of brands/manufacturers/teams. History is also full of riders/drivers always changing, for the unlucky, into declining teams and for the lucky, into teams that are on the rise. In 2007, Stoner lucked out by landing in a team that just happened to have the perfect bike and tyre package for him. A team that had methodically set about working their way to the top in the new era of 4 strokes. In my somewhat worthless opinion, that team was at first caught out by the success but then went on to a) listen to all the commentators in regards to why can't the second bike win, and b ) get greedy wanting the second bike to win with someone of the correct nationality. Since this time, once again in my opinion, they have spiralled down from their peak.
From this position that my opinion forms I think that 2 things are happening:
1. Rossi has potentially made the first "unlucky" decision of his career and gone to a team that is on a declining trend, and
2. Stoner has made the second "lucky" decision of his career and switched to the team that is climbing out of their down period into a period of dominance.
Of course trends can be broken by extraordinary circumstances and Rossi's career has at least shown that he is 'extraordinary'. However each year his career moves into a different faze or perhaps even 'trend' as can be highlighted by the unfortunate or unlucky events that are certainly different to the narrative of his career before the 3rd race weekend of 2010.
As with all stories that achieve critical acclaim, the observer gets drawn into the climax as it approaches. Let us hope that we as observers are satisfied with how the climax treats each of the characters for many a good story has been unkind to a character not of our choosing.