they use different technologies, up to a point. to me, cdrs are more (seemingly) stable and sensible, also i can get them to work. plus, why would you want to wipe a CD once you had used it? you're either doing a backup (which you won't want to wipe) or your copying something for somebody.
i've always used cdrs and haven't ever needed to use cdrws so, why should i change?
i will look into dvdrs too sometime, but again, don't see the point for me personally of using dvdrws if such a thing exists.