In a round-a-bout way, I think this actually is the real issue Raleigh is addressing. Their sewer treatment systems have to handle both solids and liquids to EPA specifications, and disposing of the solids is more costly, especially as EPA ratchets up the regulations. Banning garbage disposals won't do a thing to keep grease out of the system, but it will reduce the amount of solids they have to deal with. They may be trying to put off rebuilding their waste treatment facilities to meet ever-expanding EPA standards...
Or do you want the Ganges? Or some Mexican river?
Yes it may be what you say -- that this is Raleigh's way of getting effluent numbers under the stricter regulations. But the stricter regulations are helpful, although not without good questioning.
Me, I like a glass of cool clean water. That's why I like my well!