Add to that the idea that the middle class is perhaps the most profitable to sell to, you've got material highly targetted towards that group.
Exactly...can someone tell me which publishers are targeting their books to the extremely poor? I can imagine that wouldn't exactly be the smartest marketing decision. Personal development/self-help is a business, afterall.
I grew up poor and I don't know if that has much to do with it but the 7 Habits was useless for me, too. Also it seems that a lot of the popular personal development books (especially those written by men) are geared toward people who work in sales-- not my thing at all. Tony Robbins also leaves me cold. I find some of Steve's articles useful but I have to say I think he might be stretching the whole "I wasn't always like this...there was that <i>one</i> semester in college when I slept til noon..."
Well this is a rather unfocused reply but there it is.