I think it's like Scheckter and Villeneuve in 1979, Villenueve was the greater talent but had less experience and fell behind in the points by the halfway point of the season. Ferrari then backed Scheckter for the title as Red Bull should do with Webber in the hope that Villeneuve would get his chance again someday. With Vettel, I'd say it is far more likely that he will get another shot at the title further down the line, whereas for Webber, this may be his chance.

A very good example (though you speak as though Button is out of the title battle).

Ayrton Senna: WDC 1988,
1989, 1990, 1991
McLaren: WCC 1974, 1984, 1985, 1988, 1989, 1990, 1991, 1998,
1999, 2007McLaren: WDC 1974, 1976, 1984, 1985, 1986, 1988, 1989, 1990, 1991, 1998, 1999, 2008