While we're talking unsubstantiated rumors and downright fabrications, allow me to toss one out there.
One possible explanation for the reason the Play Store isn't accepting backorders on the Nexus 4... possible retail launch. They may want to save a Nexus-7-like debacle with people backordering units then finding them in the retail stores and shipping back the Play Store one unopened (or in some cases opened).
The UK had Play Store orders and Carphone Warehouse (a UK retailer) is talking an "exclusive" on a white one. I don't think it's that much of a stretch to think these things might appear in many of the same outlets in the US that had the Nexus 7. Staples, etc.
So, again completely made up by me and not based on even a hint of a rumor, I'm thinking it might just be possible in the coming weeks to tootle on down to Staples and pick up a white one, and then when the stores are well-stocked with white ones, the black ones will come back in the Play Store again.
And they managed the Nexus 7 at the same price at Staples as it went for in the Play Store, why not the Nexus 4?
Imagine getting these units on the shelves next to the prepaid GSM SIMs. "Would you like service with that?"