Well I'm sure someone will have more specific details of this, but the quick response to that is that some years ago when it was clear that the higher capacity of a DVD would make it a potential replacement for CDRW drives, different groups tried to come up with their own standards for implementing read/writing capability on DVDs. The "R" standard itself is standardised, but not the RW capability I guess.
What I do know too is that Sony has just come up with a drive that has compatible with many of the RW standards right now, with the notable exception of DVD-RAM; which unfortunately is the standard I have on this DVD Drive I'm using!

Rob