I don't think it's necessarily caving in as such. It's important to weigh up the value of the player to the team and who might potentially take him from you as well. United broke the bank to keep Rooney who in turn proved his worth at the business end of the season, it was a gamble but one well worth taking because of his quality and status within the team.
If there is any truth in this alleged 20k extra that Nasri wants then relatively speaking it's hardly worth taking the high ground over. Our model is too rigid for a sport full of mercenaries.