Firstly, they're incredibly easy to search. Would that other shopping sites had such fantastic search options!
Secondly, the prices they offer are usually the same as or lower than you'd get anywhere else. On many occasions I've done a price check, going to the website of the company listed as the Seller on Amazon, and the Amazon price is the same or better. A general "shopping" Google search usually yields the same result. (Comparing apples to apples, of course. You can find cheap junk anywhere, but if I'm trying to match the product and quality, Amazon scores most times).
Thirdly, they have a fantastic ethic and stand by everything they sell. To me, this is priceless and they have built up such a level of trust that I choose to buy from them rather than the seller directly JUST so that I have the back up of the Amazon promise. Even if the Seller is selling cheaper on their own website. Trust is worth more than a few dollars. Obviously, I'm not stupid, if the Seller is quantifiably cheaper, I put the item into my Amazon shopping cart and then just watch and wait until the price comes down. :)
After hundreds of dollars' worth of purchases, I believe that Amazon has earned my trust and my loyalty. Added to that, they're just so convenient, it seems automatic and natural to refer to them any time I want to illustrate a product. If I'm talking to friends or family about something and want to show them what I'm talking about, just in conversation, not to sell/buy and item, I use Amazon to look it up. It's even easier than Google when you're talking about products, or music, or DVDs, or a host of other items.
In full disclosure:
Update to disclosure: Amazon was kind enough to accept my application. In accordance with their requirements, please be advised as follows:
“No 4 Letter Words is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.”