I really don't think it is the only way it can happen and I can see why the suggesting of it being 'ambition' is disregarded. The fact that most of us just want(ed) Wenger to be a bit more flexible in his approach (if he can!) suggests that for all the money that they spend you can still compete on some level. It doesn't have to be spending gazillions every transfer window and nor, in fairness does it just have to be getting players bought for more (relatively) conservative figures and youth players. It could be that supporting a club which has always been in the Champions League skews my perception a bit but really, the league we're in is a cash cow too.
I concede however that having owners that want to invest money in to their club, taking a long term approach is nigh-on impossible. I'm just pointing out, how they are doing it (with effectively unlimited sums) doesn't have to be governed by a feeling of it being necessary.