The thing that makes this whole thing different is that the excise tax is imposed on the transaction between (for exmple) Delta and MCI, not between MCI and the customer. Ehen you go into a restaurant, the sales tax is on the transaction between you and the restaurant, where passing along the tax is ASSUMED even if not stated in the price.
For MCI to pass along a tax IT was obligated to pay based on its purcahse of FF miles from the airline is no different than if they tried passing along social security taxes on its employees, water bills at its HQ or sales taxes on its purchases.