Here's an update. I'm the one who got my order discontinued at OnSale. I bought from buy.com, and they've reported that they've shipped my order.

FWIW, I think theory #1 from Phi sounds very believable. The SKU could be changing because of the new OS.

P.S. I wasn't trying to spread misinformation. That's why I pasted in the exact wording from OnSale.com. The truth behind their message is left as an exercise for the reader.