I think he delayed crawling because he could get wherever he wanted really fast by rolling.
Actually, I believe I have read that this counts as "crawling," as does scooting around on rear or belly. All those forms of locomotion require coordination of a certain level that is similar to crawling.
I think you do have to watch for right-left coordination issues in these kids, because a kid who never does anything that requires coordinated right-left movement may have trouble reading. (Not a problem for yours!) But I think a creative kid who figures out an effective way to get from here to there doesn't get dinged for doing so.
