I recall an alternative assessment of this story. I read that Ferguson had planned to retire at the end of the 2011/12 season. He did not after the manner in which we lost the league to City right at the end of that season.
Sir Alex was aware at that stage, City under Mancini, did not have the experience to retain a title. Therefore, he knew he just needed Vidic back (after the knee injury sustaine against Basel) and a Premier League striker who would guarantee the goals in order to win games where they dropped the season before (Blackburn, Newcastle, Everton etc).
Step forward Robin Van Persie. Van Persie was the subject of interest between City and United, but it was quite early on during the summer, he chose to join us. Arsenal knew they had to sell as he was on the last year of his contract and he was not going to re sign.
Arsenal were holding out for the highest fee, as they were entitled to do. In order to push this along, Ferguson allegedly phoned Wenger personally. During that conversation Ferguson said along the lines that "the boy wants to join us, we will give you decent fee for him, just tell your board to sell to us." Wenger agreed. He was also fed up of City buying all of Arsenal's players on the cheap when their contracts had run down ( Clichy, Sagna,Adebeyor, Nasri).
Apparently, Wenger went into work the next morning and the first person he told of the conversation between he and Fergie (instead of the board) was his assistant Pat Rice. During that conversation, Wenger said "I have agreed to let him join United, but the strange thing is he (Ferguson) has never done that before ( phoned him personally) , I have a feeling that this is going to be his last year."
This was obviously before the January referred to in the book and before Lady Cathy's sister Bridget passed away. May they both rest in peace.
I think this is plausible, but I obviously do not know if it is true.
Anyway, back to Moyes, he was totally useless a dthe job was too big for him and Mourinho with his contacts could have assembled a better squad and won another title against Pellegrini.