Also, given how much effort, time, manpower, money, sweat and tears is given by teams to try and win races let alone WDC's id say winning one is more then enough repayment, Mclarend didnt sponsor him to be kind, they arent Mother Teresa, they did it to get a return from him in the future, they got their return in 2008, and in the other years Hamilton has won races for them.
I agree with what you say but I also agree with what Bud says (surely a sign of impending doom). Getting his one title so far and gathering decent points for the constructors has reapaid Ron Dennis's faith in Hamilton to an extent. Given the amount of time and money spent on a kid in go-karts and bringing them through the ranks into F1 is a huge investment and a risk. McLaren will want more than one title out of him and they are going to want to win the constructors championship whilst Hamilton is in one of their cars.
The same goes for Vettel who Red Bull invested in way before he was in F1. Obviously you take into account marketability of a driver and the various PR duties that drivers are obliged to do.
I didnt say Ferrari was a given title either, id just like very much to see Hamilton driving for them.
Linking into the above (and this goes for Vettel and any other driver who has been sponsored/invested in by an F1 team since year dot), part of me wonders if it is entirely up to the driver if they change teams. The team which has spent a fortune on a driver since before their F1 days will want their pound of flesh and I can't really see an F1 team wanting to give the driver the full control of their future, especially if the driver concerned has a lot of potential. The team will want a fair bit of loyalty from a driver but the driver will obviously want to get the best possible deal for themselves, which is fair enough.
Probably best to give an example. I looked into applying for as a driver to Stagecoach a while ago and getting put through my bus license. In return, I am obliged to remain at Stagecoach for 2 years. If I were to leave before then for a better deal I have to pay £1,400 for my training. I would imagine it is kind of the same idea with drivers like Hamilton and Vettel only the sums involved are a lot higher, with the goals set by the team being championships, points or finishing targets. Maybe I'm wrong but it seems plausible.
As for hamilton going to Ferrari, not whilst Alonso is there. Neither driver would want a repeat of 2007 and Ferrari would not want to fast drivers - they want a fast guy and a "team player".