Wii keeps climbing in sales.. because people are getting rid of them? Buahahaha... riiiiight. (Not saying there aren't some people dissatisified with it, but to think this is the majority is rather foolish.)
A hot market item, that is in big demand (regardless of your opinions of it) at a good entry level price, and there's no chance at all that people are... I dunno, buying them up in masse and selling them for a PROFIT on Ebay? I mean, I think that's what people do on eBay right... sell things to make money?
People are probably going to eBay for PS3s in hopes they can find a deal on them. If you live out somewhere where there's perhaps only one big chain store, and they have a set, dead 600+tax price... and you have the internet, why would you NOT look for deals? On eBay, people do buy things in quantity for lower prices than what you pay retailers, and they do try to sell those things for a profit.
Edit - Added the ( )'s stuff.