You seem mad about the idea of designating neighborhoods within downtown, why? Thats a smart thing to do, as there are different neighborhoods that make up greater downtown.
Its part of the Urban Form Project, here's a post from the DVC about it:
http://downtownvoices.org/2010/01/29/phoenix-seeks-public-input-on-downtown-code/
Since Downtown is made up a variety of different neighborhoods (or 'character areas') each area has its own specific type of zoning. Biomed is different from warehouse which is different from Evans Churchill, etc.
You can see this PDF for more info on the character areas:
http://phoenix.gov/urbanformproject/dtplan03.pdf
Here's a map of the character areas if you dont want to look at the whole document: