Van Persie has been a revelation at United since his move from Arsenal.
"Since day one, when he joined, he has done very well," Stam told ManUtd.com. "Although I've heard people talking about him not scoring for a while, he's scored a lot before that and, when he gets chances again, he will score goals for United in the future.
"He's done exceptionally well and is a world-class player who has proved himself in England really well since he left Holland. So everyone has got a lot of respect for him for what he's done in his career.
"Robin has been very important for the club. It's hard for strikers to score in every game and to finish off every chance that they get. It's not like that in football. The opponents always know the quality of the strikers so, if van Persie is scoring, a lot of other teams will be marking him with two defenders and making it hard for him to score.
"But it doesn't matter as he's then taking a lot of attention away from the defenders and, if someone else scores, as they have been doing, then it's okay."