It's because ever since we were babies, like mentioned earlier, we've been saturated by the sound of the major scale. Radio, video games, and the biggest one: TV. Think of all the comercial jingles and whatnot. But really it extends to everything. Think of a doorbell. Ding Dong!

Consider this... those who have been brought up in western culture find Indian music almost excruitiating (those 22 note chromatic scales aren't for the faint western'er heart), but to them, it would sound as perfectly normal as the western chromatic scale.

I read something interesting lately about whether or not babies are born with a sense of music, like if it's inherent or not. They tried testing babies by playing a major scale and then playing a wrong note and seeing if the babies reacted. The results were that the babies overwhelmingly responded and could identify the off notes. Is this something inherent to them? Maybe they've already been conditioned to recognize the scale ever since the womb... who knows. Any thoughts on this?