This conversation is about longer-term happiness, not the brief rush you get from buying something or getting something in the mail. I think there's a strong argument that in that sense of the word "happy", Amazon actively contributes to the unhappiness of their customers.
They don't optimize for happy customers. They optimize for being the place you go to buy things online first and profit. Oddly, they bought Zappos which is orientated to customer happiness.
Amazon is quickly becoming the walmart of the internet for me. I'll buy from them because its easy but I don't expect them to sell me a quality product.
Also, I doubt that product quality is a factor at all when they put something is a store. I would like to think that I buy things from people that care just a little bit about me and the things I buy.