Can't edit my post so I will add what I was going to put here. Brevoort has always said that he hated the name 616 or had a general distaste. I wont't be able to provide proof of that but I've seen him say it on formspring multiple times.
It's just be like the current DC Universe going through a Secret Wars style event. But Geoff Johns and others don't like the name. So they name it something else.
Originally posted by StiltmanFTW
They never liked the 616 name.Thanks, Scot. Makes sense.
Going to post it again here since the reply took it to the next page.
A bit more to discuss on the whole 616 or "Prime Earth" stuff.
Nrama: One thing that did seem to be intentional, that you also mentioned, is the placement of Miles Morales into the Prime Earth, as we’re now calling the main Marvel Universe.
Brevoort: Technically, we’re just calling it “The Marvel Universe.” We call it the “Prime Earth” in Secret Wars because we had to call it something and we didn’t want to have a number. We really wanted to retire “616”, despite [editor] Jordan White’s protestations.
We’ll have all the readers of Web Warriors showing up going, “But, but, but, in issue 1 there’s a locator that says ‘616’!” And yeah, you can decide which one you want to believe – Secret Wars, or Web Warriors. Web Warriors #1 came out before Secret Wars #9 – I wouldn’t have let them put a locator that said “Prime Earth” because we weren’t there yet.
But really, it’s just the Marvel Universe.
http://www.newsarama.com/27626-brev...za-analogy.html
So it isn't a new universe, rather they just want to retire the 616 name.