The more it sells, the more they lose. The percentage of market share they may gain by doing this in the short run won't justify the loss.
I completely disagree. Sony's wasting the six million lead that they've gained on Microsoft by not follwing and doing the same thing.
$300-500 million over the holiday season is a lot less to lose than giving up marketshare. More people will have the Xbox One, so devs will further gimp PS4 versions to maintain Xbox One neutrality, the money lost would be mad back with only a few games or XBL/PS+, and since more people own the console there's the whole view of how many were sold as well as friends who want to get the same consoles as their friends.
Microsoft might be losing money in the short run, but they're gaining far more back in the long run. You might as well say they have gained money by doing this rather than losing money,.