OK, I'm not going to chase this around in circles, but here goes: No-one will sell BELOW the price of replacement, because if he would, he is better off simply not selling. I should have been clearer: the MINIMUM is the price of replacement.
OTOH, No-one's in a hurry to take a loss on buying gas high and selling low. THey'll wait to see that the price of gas doesn't bounce right back. No-one is going to be saying, "Woo-Hoo! I sold all my gas!" when they sold it for less than their costs, and then they have to refill for more than their sale price again.
Thanks - makes sense, but it does follow that they are making increased profits by being cautious in their pricing (at our expense) - but then that's business eh?