Okay, you're right, the Parelli Program IS supposed to be entirely successful WITHOUT human instructors. That is really unrealistic! I heard they've tried to make it more "user friendly" but really, dealing with horses can be quite dangerous — to start with just a DVD--!
That said, I STILL haven't met anyone who hasn't had one-on-one sessions at clinics or in lessons. These trainers often leave their phone numbers: that's what I meant about calling. The latest trainer to come was David Lichman, who also evaluates videos (my friend has sent a couple in). You don't have to be a member for this. (You don't even have to pay, if you don't like the advice.)
I think the cult-like part is because of their Play Days, when they all get together, etc. I agree it's kind of cultish, but it's fun, and unlike most other trainer systems (are there any?) it's a social event, and for many, it's an encouragement to keep trying to improve.