Once again, I do not like Ryanair. I avoid flying with them and I don't even want to buy their shares...BUT
You cannot include the cost of an £18 wheelchair assist in the price of a £15 ticket. Even if you pay something approaching the normal price for a ticket, £18 knocks a hell of a hole in the profit-but at least there is some leeway.
This cost, and who pays it, was bound to come to the courts sooner or later so lets see how they rule on it. Perhaps the rail firms and bus companies will all have to provide free lift ons and buggies, but I doubt it.