I used to question most of those people too (and still do), but someone explained it fairly well in response to why patio11 did this with his drip marketing class: it's simply a scale out strategy. Given the available time an expert has, one could make $X as one person just doing it; with consulting and teaching others, you might reach 5 people in a year; but by turning that learning into intellectual property that can be distributed (as a class, a video, a book) you might be able to reach 100x the people.

That said, there are certainly gurus who are merely selling hope, often because the easy money has been made and they can wind down what they've learned because the edge no longer exists.

You know what I can't figure out though? Why is Mark Cuban shooting a commercial to pimp lame shoes?