Sony has been in a lot of trouble even since before the PS3 came out. They decided to amp up the processing power of the system fairly high making it rather expensive considering the components alone. This was supposed to outdo XBox, which it technically does, but the problem is developers may or may not be able to take full advantage of the system's full capabilities. So long as the games are only on par with XBox and occasionally somewhat better what's the reason to purchase the more expensive console? Fewer game developers, particularly larger companies, are willing to maintain exclusive contracts now as well so there is less likelihood there will be many popular games you can only get on one system. BluRay was a big gamble for them too since they had no idea whether or not it would become a standard or die out. So far I don't think it has caught on strongly enough.
XBox 360 came out long before PS3 and microsoft has already made the money they needed off the box and can afford to continually bring down the price and undercut Sony. I'm pretty sure their box is much cheaper component-wise aswell.