Not that it really matters much,
but I'm pretty sure this isn't actually true. DME is a separate, contracted service (Mears) and their systems are not integrated with Disney's. When you make your DME reservation, you, or a Disney agent, are really just filling out a form that is sent to DME (Mears). Disney does not store this information as part of your file. That's why you can't see your DME info on your
MDE account, and Disney can't tell you if a reservation with DME even exists, let alone change one. They just tell you to call DME or put in another request (or they may take the info and submit the form themselves).
The DME folks can look up your resort reservation to verify eligibility, but they're merely accessing Disney's reservation system directly in read-only mode.
I could be completely wrong on this - but from several conversations I've had with the great people at DME, and my understanding of computer systems, this is how it appears to be set up. Plus, this way would, by far, be the cheapest way to do it.
Steve