the trouble is that RealD have the largest share of the 3D equipment market because they offered all the 3D equipment free to cinemas but then they get a licencing fee per ticket sale, which makes up some of the surcharge. the film distributors also consider the surcharge as part of the ticket price, so they also take a cut.
so say the surcharge is £2.00, of that the distributor will take anywhere up to 60% (£1.20), RealD will take probably another 60p for their licencing fee so that is most of the surcharge taken up really.
other 3D systems (master image, xpand, dolby 3D) don't all charge a licencing fee but a hefty upfront cost of equipment and installation. you'll find in some cinemas with some of those systems they charge a much lower 3D surcharge, or in rare cases none at all.
cinemas with a realD system can't take away the surcharge without cutting into their own share of the ticket price.