It's just that the auction experience can become somewhat addictive, that's all.
Unfortunately, due to the prohibitive amount of money that was paid for PayPal, the company has needed to dollar and dime everything they can get out of the business at the expense of those who were the "power users" and had successful symbiotic businesses. It's also the reason why Ebay coerces you to only pay via PayPal at every opportunity, rather than use another method. They desperately need to make the PayPal thing "work".
I don't think so. And as for the addictive experience you are quoting, which online shopping portal does not seen addictive? I bet the ones that don't, actually have zero consumer retention value. What say?!