Most kids by age 4 are asking for anything they see on tv or in the store. Not mine. I'm not sure why though. Is it because of his delay? I don't think so because we'll go to the store, we'll look at toys, he'll like something, but he doesn't ask for it. He doesn't quite grasp the concept of Santa, probably because he's only done two visits with Santa and both were when he was very young. He doesn't even ask for things for his birthday.
Perhaps it's because he gets very little commercial-ridden television. We watch Nick, Jr. (formerly Noggin) and PBS Kids. Neither of which have commercials for sugar cereal, toys, or other crap.
We've generally tried to stay away from character toys, which living in the Orlando area was tough at times, but I'll bet he has less than 15 toys/plushes that are name brand. If he saw things like Spiderman or Transformers, it was at school or birthday parties.
Yet, he doesn't come home asking for it.
Maybe it's because he doesn't get a lot of things, maybe he just knows better than to ask. He's a very appreciative little boy. As my MIL put it, he doesn't care if you gave him a ride-in car or a box of new crayons, he's happy.
He'd rather have a wagon to ride in with his baby brother. He's discovering all of his old baby toys and showing Henry how to play with them. (some days better than others)
Mostly I think it's a combination of all three: his delays, commercial-free television, and he gets what he needs, not just what he wants.