Ebay's best asset is it's search engine. Just type in all the variables on the item you are looking for and you get all the results from everything available. With some of the online retailers it can be confusing with some of the drop down menus and navigating to exactly what you want.

Add in that Ebay gives you a picture of the exact item you are buying, I can see how some people are lazy and don't shop around. Sometimes I will use Ebay just for it's pictures to find exactly what I am looking for and then go to the online retailers to purchase it. Maybe some people don't want to take that extra step.