You know, it could be expensive and sought after because it is a bloody awesome school?
My DH and I are and interesting case - he went to Eton, worked hard, got in to Oxford, and now has a very successful career in the City. I went to a shitty comprehensive, worked hard, got in to Oxford, and now have a very successful career in the City.
We come from completely different backgrounds, and had completely different schooling, but we've both ended up in the same place. I know how hard he worked, both at school and university and now, and I would be outraged if it were suggested that he got where he is because of his school, just as I am when people suggest that I only got into Oxford because of state school quotas (I'm not joking).
He is also pretty embarrassed when he has to reveal where he went to school, as he is worried that people judge him on it, without getting to know him first. Isn't that just as bad as judging someone on any other superficial criteria.
If you visited Eton you'd see exactly why people want to send their sons there - it is the most amazing school. The facilities are incredible, and the teaching brilliant, but most of all, it is one of the most open, inclusive, non-judgemental places I've ever seen (oh, the irony!) There are pupils there from all over the world, from all religions, from all backgrounds (including lots of scholarships). They are taught to be polite, well adjusted, confident, self-sufficient young men.
If I can afford it, I'm sending my sons there - not because of what it will do for them in the future, but because of the wonderful time they'll have in the present.