It is possible because of two main reasons.
1. The Xbox 360 will be relevant for longer. It looks like it'll not have a replacement on the market for at least a couple of years and it is unlikely that the next generation games will make the 360 look completely obsolete visually unlike what happened to the Wii. Beyond this the Xbox 360 has media features outside of games which will make it relevant to the market at the $100-150 price point for longer as a media extender box. Since it isn't performance but budget which limits consoles these days I don't believe that the median games in 2013 whether they are PC or console releases will make the current generation look terrible, unlike what this generation did for older PC and PS2 games.
2. The games market has grown so it is quite possible that in 2-3 years time we'll still be talking about how well it is selling as keeping the older machines on the market gives the console makers free reign to release machines which are $300 or even more expensive because they can consider the low end demand being met by current generation consoles.
Tease.
