I know you like to be positive Matt, but come on! If this accommodation was dirt cheap (which it is not) then I would be more inclined to agree with you. However the price is still a premium, and towels are the least you would expect after a bed.
Having stayed in more than a few "budget" type hotels in both this country & France, I have never been charged for towels. Many of the said budget type hotels don't even take a credit card hold at check-in either.
Towers should include the towels for free for the Sheds and just deduct a fee from your £50 credit card hold for any that you decide to "liberate".
The towel fee is all the more laughable as the queues to use them / get them wet in the facilities block are clearly going to be stupid during the morning rush.