I'm not sure how I feel about this.
On the one hand he's the salavationist who brought the club it's longest period of success ever, and rightly is considered the greatest manager of all time (so far)
On the other he's 83yrs old, if he has been flying around the world as a club ambassador and doing all the things that entails, he deserves a good rest.
Personally I think the salary issue is not the reason, to me it's the need for a new era, Sir Matt hung around the club for too long, and was still considered "The Boss" even when SAF took charge, SAF himself said that players would go to Matt, before they would go to him, perhaps there are similar issues going on behind the scenes.
For what it's worth, I thank him for all the great times he gave us, all the trophies and all the spats with the press, it was never a dull moment, I wish him all the best and hope that he spends more time with his family and enjoys what years he has left.