I think this is just preemptive strategy on MS part. They have planted the seeds of $600 in everyones heads now so when they come in at $499 some would say it's cheap.
I think they will come in at $499, no chance they will be at $399 if they are going to have all the stuff over they PS4 thats rumored. Unless they choose to sell it at a loss. Which I strongly doubt MS will do.