As you say, Amazon makes it very compelling and easy for one to buy books - the recommendations based on your browsing history, past purchases etc. and 1 click purchase is just superb. Also, there is a wealth of reader reviews which gives you great confidence what the book will be like.
I also love the huge community and discussion boards - filled with recommendations, many from indie authors. The whole indie community is another bonus - there are a lot of quality books priced very affordably, and you can often pick up a few good reads for less than the price of a cup of coffee.
Finally, it's amazing how Amazon keeps giving away the promotional freebies - it's a great lure to bring you back to their site again and again, which will lead to incidental purchases.