From a pure gameplay point of view Career mode looks like the sort of option that should be unlimited (or at least, some arbitrary high number, say 20 seasons). Given that they already have a 7-yr career in 2010, I don't see this as a particular problem. It doesn't even need to be particularly dynamic in the later years - at least, no different from the previous years - just a slightly more realistic contract progression that allows you to move up (and maybe down) year on year.
However...
From a design perspective there are a number of other factors at play. Particularly Multiplayer and the game franchise. Online play is where things are going. Certain gametypes lend themselves very well to online play - racing, other sports, shooters and so on. With budgets tight, development is going to focus on the growth area. A multiplayer career mode built and supported in-game would be the greatest wish for a growing number of players. For many, once you've played online (and not just F1, all sorts of games), then single-player career just doesn't cut it.
With regard to the franchise, the cynic in me says they dont want players hacking their way through 7, 8, 9, 10 or more seasons come the autumn, with a new release on the way. I suspect they want career mode done and dusted by the summer and people playing online.
Cheers.