Ferguson's letter is contained in the Premier League's 64-page review of the 2012-13 season.
"The club's commitment to investment at every level shines through. Top-class players, both purchased and developed; wonderful facilities at Old Trafford and Carrington for players and fans; community programmes that place us at the heart of the community locally and farther afield - the club has set a standard in the Premier League that others strive to better.
"Sometimes they manage to! Those challenges, season after season, spur the best on to be better."