United's on the field success under Ferguson allowed them to become a bigger and bigger global brand and arguably he was spending the money that he had been influential in generating. Don't get me wrong, United were always a big rich club but the extent of what they've been able to spend is down to what sponsorship deals etc they have been able to harvest from on the pitch success, plus the money they have made from constant champions league qualification.
And whatever we think of Wenger, it's fair to say that when he goes he leaves the club in a monumentally better state than it was in when he joined us. And to dismiss and downplay his role in that would be grossly unfair.