This is only a good thing. I still see very few iPhone 5s out in the wild (besides my own.) I have to think the demand is there, but people still think it's too hard to get.
I think a lot of people are sticking with their 4 and 4s. Certainly most folks won't upgrade from a 4s. But I know folks who are trying to get their 4 to bridge to the 5s. I just put a new battery into my GF's 4. It is giving her a new lease on life with that phone. Also, some folks who bought the 4 still haven't made it to through their two year commitment. So they aren't due for subsidized 5 yet.
That isn't to say the 5 isn't going to be the best selling phone out there. It is. But that you might not see it for a while and it may not outnumber the 4 and 4s out there for a really long time.