Well, from what I’ve seen, I don’t really think that there is a lot of “teaching yoga” going on even when you HAVE a teacher. Since I’ve gotten back into yoga these past several months, I’ve noticed that, at many yoga classes, they aren’t really “teaching yoga.” It’s more like they’re calling a square dance. “Now we’re going to do this posture. Now we’re going to do that posture.” And if you don’t know the posture, then you are expected to just look around at your neighbor and try to put your body in roughly the same position. That is, apparently, considered good enough.
This is the single biggest shock to me since I’ve gotten back into yoga this time around because the first time, I was learning Iyengar yoga from a very, very highly qualified teacher who went into incredible detail about the correct postural alignment of the asanas.
And now I’m doing Ashtanga on a regular basis which is, essentially, a self-taught system. They will go through the postures with you a few times and will correct the posture if they see you doing something wrong, but you’re basically left to learn it on your own.
The yoga workout in the P90X system is, from what I understand, a perfectly legitimate Vinyasa-style workout. Since you have a video that you can return to again and again (and, presumably, the postures are demonstrated correctly), I’d say that you might actually be getting MORE detailed instruction than you get with a lot of yoga classes, depending on how the instructor teaches.