Morally, I think this is wrong.
Legally, I don't know. I don't think EU has any regulation pertaining to duty to care in case of tarmac delays (only airport delays) and I'm not sure to what extent does the US regulation apply to this case.
However, DOT seems to indicate this should be covered, so you have grounds for complaint - worst case they will tell you this situation is not covered, best case scenario, you get some redress.
During a tarmac delay, airlines must provide you with a snack, such as a granola bar, and drinking water no later than two hours after the aircraft leaves the gate (in the case of a departure) or touches down (in the case of an arrival).