Amazon is not only for stuff they themselves sell.
Others and even individuals can sell their stuff through amazon.
With amazon, if you are log into your account and add the item in your cart, then the item you added in your cart stays in your cart unless you remove it. Maybe this is what malhortaraul wanted to say.
Its not really inconvenience as you do get confirmation page before you are taken to checkout.
Even big shops like buy.com, tigerdirect etc sell through amazon. This is really beneficial to someone like me who do use mail forwarding services. Shops like buy.com / tiregerdirect do not accept Indian CC directly through their portals. But you can buy though them using amazon and use your indian cc and get the item delivered anywhere in the usa or directly to you if its non electronic item.