Fletcher is a red through and through and has been out of actions due to entirely different reasons than Nani - comparing the two is beyond stupid. Not that I expect you to see this.
Nani is not a Manchester United fan, he's a Manchester United player who is in the worst period of his career at the moment and on his way out of the club at the end of a season where he hasn't made a contribution at all; due to injuries, poor form and lack playing time.
He has been a part of title wins in the past, he knows what real joy is like, when you have had a part in securing said title. That wasn't the case this season, and thus he could either fake the emotions or he could stay in the background and pay his respect to those who actually played a part. He chose the latter.