In my mind, the fanboy-type reaction is little different from any other consumer attachment. When we buy something, we believe, or at least really want to believe, that we made the right choice. Our subconscious mind works really hard on this stuff, and the more you spend the more it matters. There's a whole bunch of psychology behind that (The Paradox of Choice takes an interesting look at the subject), but the result is a strong defensive reaction when a purchase is criticized or a product's value is called into question (even a little bit).

The iPhone, as an alternative product that I did not buy, must be inferior in some way or I must have made the wrong choice. But I didn't. I made the right choice. I don't regret a thing. I bought the superior product. I'm a smart consumer. I love my Droid. It is the best phone ever.

And there you have it.