Sony has been a sinking ship for over a decade now. And while gamers are gonna be happy about Sony presenting the PS4 as a gamers-first platform, let's remember that PS2-level numbers are going to be a fairy dream for Sony.
Why?
First, Sony is living in a stagnant mentality (like many of their Japanese cousins). They're not a leader anymore when it comes to technology (except professional film cameras maybe), services, infrastructure and even the quality of games. Yes they have more studios, but most of their IPs suck (Killzone, Uncharted etc. I mean c'm on) and they keep losing money due to mismanagement (FFXIII versus, Last Guardian etc).
Second, MS consciencely chose not to aim for the most powerful machine out there. For starters, 8GB GDDR5 RAM cost around ~$145 on the markets (directly from the supplier for mass production), while 8GB DDR3 costs ~25$. Guess who will be able to have better price flexibility? Not to mention the Yen is very weak which in return is going to be bad for their own domestic market.
Third, MS is thinking farther ahead in terms of services and infrastructure (cloud computing could develop into a big thing), and also spend more on R&D than Sony and Google combined.
While this is no guarantee for XB1 to horribly fail, at the very least MS is better bolstered against shocks and also has a more diversified portfolio. If games fail, they always have their TV and interactive TV-stuffy, and vice versa.
Sony only has those games. With the current economy and the low demand, people are definitely going to be more picky. Sony provides more quantity, but that's not what people necessarily want anymore. More more more buy more play more play everything is a game that MS chose not to play any longer.