No you weren't fleeced if you wanted the peace of mind that even if you don't turn up at -4 hrs to STD you will have seats together. Quite obviously there are an finite number of seats on an a/c and without paying the fee you would have to be among the early check-ins to be reasonably sure of sitting together. If a lot of other pax have paid the £20 then there might not be many seats left allowing you all to sit together even if you check-in early.
Re the skis, you are correct that the money goes to the Tour Operator and not the airline. It doesn't guarantee carriage, and it doesn't prevent you paying for excess baggage either! My understanding is that the Tour Operators used to get commissions from the ski hire shops in the resorts, but as pax started to take their own skis with them the revenue declined so they started to charge for the privilege of taking your own skis. The airports, airlines and handling agents who have the *rse ache of getting the skis from c-in to the aircraft get nothing extra for their troubles.