Hi John
I have heard that most of the plethora of asanas known today are a recent creation, but I don't know how many of them, if any, come from ancient traditions. I completely agree - classes that teach asanas only and call themselves 'yoga' are far off the mark. The essence of yoga is working with the mind. At the beginning of his Yoga Sutras, Patanjali defines yoga this way - "Yoga is restraining the thought-streams natural to the mind / Then the seer dwells in his own nature" (1.2.-1.3.)
There has always been a concern with posture however. The same Yoga Sutras say "The eight limbs of Yoga are self-restraint in actions, fixed observance, posture, regulation of energy" etc (2.29).
I agree with Dogboy and Charliedog in that asans have their use. I am enjoying mine a lot more since restarting my meditation practice. Without meditation, I was getting to a point where they seemed pretty useless, but once the energy builds up, it's good to have a tool to help smooth it out.