You have to factor in that the results in the last years of the AF era were possibly the greatest overachivement by any squad in the history of the Prem. Moyes inherited champions but just look at how weak that squad was - Rooney was their star man but he had aged badly. The rest were average (Fellaini, Smalling), some absolute wank (Cleverly / Januzaj) with the better ones well into their 30's (van Persie).
That period must have given Glazers a very false impression of what it takes to do well over time.