LeQueen, glad to hear you've looked at the book before coming back to the thread however...
I think UP appeals to a certain type of person - well yes, different strokes for different folks, no? GF appeals to a certain type of person, go with what fits in with your family.
The book makes them feel secure, it has guidelines and structures to follow. Er, no it doesn't. Are you sure you picked up the right book? Half the issue is it doesn't give you guidelines and structures, which is why there's a lot of room for (mis)interpretation.
Also, it gives them a new identity i.e. 'I am a parent who follows UP themes' it gives them a new status. Bollocks. It gives you a shorthand term to say to other parents (usually on MN) that you're not following sticker charts etc. Do GF parents have a new identity "I am a parent who follows 4 hourly feeds?"
It also encourages them to think they are the more grounded, spiritual, intuative parent than most other parents (ergo 'better'). Again, no. If it was intuitive, the book would be redundant, and a lot of the points are counter intuitive.
Then there is also the element of belonging to something, of being part of some vaguely elitist group 'that few other people really understand, and I can enjoy treating you in a slightly condescending manner as a result.' What, like the condescending manner of your posts? 
And, then of course they clearly must have quite a lot of time on their hands, a very lot of time (I wonder why) to get embroiled in long, long debates and discussions with their child, going over the same ground over and over again... As opposed to a lot of time on their hands to spend banging over the same points again and again on UP threads on MN?
And you keep saying how terrible it is that this man has written a book and makes money out of it. It is a book. Libraries have it. There is a whole heap of money in sticker charts and the like. So chuffing what?
Yawn.