While this doesn't mean it will apply again in the future, but Microsoft and Sony have sold consoles at a loss before and make up the difference with 1 or 2 game sold per system. Then add on the money being made with Xbox Live Gold and PlayStation Plus.
I still think $399 at launch would sell much better than $499. But it depends on the specs and how much MS and Sony are willing to lose per console sold. The consoles will generally sell well the first couple months, but both need a steady stream of quality exclusives. Nintendo launching the Switch with BotW really helped, then MK8D, Splatoon 2 and Mario Odyssey over the next several months after launch helped keep the sales up.