Rha and Dave - i can only assume you use the word 'pull' in a way which is fundamentally different from the definition i know. But if it helps your dancing to think of a pulling action, then that's good for you guys. But i simply can't accept that the moving foot, when it does its heel strike, exerts any force at all back towards the dancer's body.
Rha, if there were this pulling action, it would straighten the knee, not force it to bend. It bends because the dancer's momentum is absorbed by the knee.
try running in very soft mud. You will find your back foot (the one you're leaving) sliding backwards, and your front foot sliding forwards. If the front foot were trying to 'pull' you forward, it would be sliding back towards you. This doesn't happen.
Having said all that, if this mind picture helps you, that's fine.