When I first read your message, before I read a little bit about you at the bottom, I thought this must be an only child. ;) I would not worry at this point. A lot of kids don't walk until they are 12-14 months (some older). I laughed and thought first and only child when I read the message. With first children, they get so much of our attention (undivided) that they sometimes take a little longer to do things for themselves. Why do it themselves if a little fussing means Mommy or Daddy will do it. =) I remember it well with my daughter. It was easier to cry (even when we knew she could do it) and have us do it. It was not a sign of physical developmental delay with her. It was a sign of intelligence. She knew how to get someone else to do something which was difficult for her to do. I know if I could wine and fuss a little and someone else would do my dishes, I would wine and fuss each and every day.
Also, not every child crawls. Some commando crawl, some roll where they want to go, and some walk before they ever crawl.
To be on the safe side, I would call and let his doctor know what is happening so they can track it over his next couple of visits to make sure there isn't a physical developmental delay. If they think it is warranted when you talk to them, they may recommend testing. But I think it is probably a sign that you have a smart baby who knows how to get what he wants without having to work harder or do something that perhaps frightens him a little (like moving from a sitting position to a lying position to crawl). You may, also, want to work with him a little on it. Put him in a sitting position and then help him down onto his belly from that position. If you show him how a few times, he may start to do it on his own.
Good luck and I hope my message has helped.