You really can't compare the two, although their situation seems quite similiar.
First, Nintendo has always had just a couple of games that sold a lot, compared to a more diverse first party offer from Sony. So you can't say Nintendo consoles sell more because Nintendo has more five million plus sellers. While Nintendo console owners usually buy most of all top-tier first party games, PS owners may are just interested in some.
Stronger third party support for the PS3 has already been mentioned, I won't go into this any further.
My third point is the different situations of the companies. Nintendo wanted nothing more than make a profit and have a console spread wide enough to keep up their brand name. Sony is a company that has much more sectors than gaming, so they might leave the sector although being profitable, or stay in although making losses. Their situation is just more complex, so I don't know what their goal is and if they can reach it with first party games alone. I tend to say no though.







