Its actually not, if you analyze all the costs. You get a very SEO friendly store, access to Amazon's recommendation engine, review system, and a few more pretty good things. You can sell Amazon products, if you need to fill out some areas of your store, and you don't have to worry about shipping those. You also don't have any hosting fees or bandwidth fees, no matter how many visitors you get or how big you grow. The credit card processing fees are included, and there's no need to get a merchant account either, which for some people with bad credit is hard. And besides that, it saves a person who might not have a lot of programming skills a heck of a lot of time, which I think would also be worth a lot to some people.