No, you're not wrong. 10% isn't viable for most locations... for some of the older stores with better lease situations, that's probably doable but by and large it's not.
I'm pretty sure that the Xbone will get secondary preference in store layout and shelf space too, unless by some miracle it just massively outsells the PS4, which given everything we know now I doubt. It's been about 10 years since I managed a GS, and I don't know if they're still around, but the guys who ran the ship back then would probably have contingency plans at this point... however, they're probably smart enough to have seen the writing on the wall and dipped out to enjoy retirement, so no clue what the B team likely running things at this point will do.
My whole point is that even the B team is not as dumb as forum goers; when faced with a new reality where they can have one slice of pie instead of the whole pie that they'd been eating, they will eat that one slice and try to find new revenue streams to make up for the loss, instead of throwing a tantrum and putting all of the xbone stuff in the supply closet.