Cockroaches are tied in with the concept of another species (the heroes) being more evolved or superior to humans (from Mohinder's opening speech). They also are linked to the idea of a divine plan at work (as they are proposed as the true image of God). If they had just appeared randomly without introduction, I would agree that they wouldn't deserve the status of recurring element. However, their being mentioned the very first time we meet Mohinder combined with what he's saying about them puts cockroaches in the status of recurring element, at least in my mind. Perhaps future episodes will help clarify one way or the other.