B.D.
Swaddling babies while asleep doesn't stunt growth.
Babies need the security. He will "undo" himself from the swaddle when he is ready. You can find a few websites that will give you an estimated time table for development if you worried about his growth.
Here is one about swaddling: http://www.babycenter.com/408_when-should-i-stop-swaddlin...
Don't worry about it too much though. It seems like your son likes the security of it since it helps him sleep.
:-)
~B