I hate to complicate things, but there's always the possibility that some of the people in the matrix are merely programs, and are part of the matrix. Indeed, we know this to be true for the Oracle, the "frenchie", the keymaker, etc. What I'm suggesting is that it might be possible that some everyday, "normal" people are programs designed to keep people in line, or to feed them information, etc. This would inflate the population of the Matrix beyond how many humans are connected to it.
Of course ... considering all the issues in the Matrix, I don't think believability was a prime concern for the movie
Stephen