I really don't see why people here are having a go at Rosberg. He isn't saying anything that isn't completely true - he's not saying that he doesn't want Williams to win - he's saying that he doesn't believe that they have the budget to do so. I actually think the comment is more a dig at the FIA for bowing to the pressure regarding the budget caps.
The fact of the matter is that Williams simply don't have the money that Ferrari, McLaren or Red Bull have, and it will take another year of at least two of those teams getting it wrong for Williams to win another race under normal circumstances, unless they can find and exploit another loophole in the rules such ats the double diffuser issue this year with Toyota / Brawn.
At the end of the day Rosberg is a racing driver, and a good one at that. Why shouldn't he have ambitions of winning races and championships? In my opinion, if he didn't have those ambitions then he shouldn't be in the sport. He's given it four seasons in a race seat at Williams, thanked them courteously for the opportunity and now wants to move on.
I really don't see how there can be any other point of view on this matter under these circumstances, so can't understand people getting their knickers in a twist over it!
Favourite racing series: F1, Indycar, NASCAR, GP2, F3, Formula E, Trophee Andros, DTM, WTCC, BTCC, World Endurance... etc. etc.