The centre-half, 25, was called up for the first time by England coach Roy Hodgson for the two recent World Cup qualifiers.
That is almost five years after leaving Old Trafford for the Potteries.
Pulis said: "I'm not so sure Ryan would have played many games if you look at Vidic and Ferdinand.
"I'm not so sure Ryan would have made the progress at United that he's made here. He's been given the opportunity and sometimes you have to take a step back to take steps forward.
"I think Ryan would be the first one to say by coming here he's got the opportunity he might not have got because of the quality at Old Trafford.
"He goes back as an England squad man and captain of the club. I'm sure Sir Alex is pleased as well that one of his players has come through and done so well."