When I had a engine warning light appear on my cars dash last year I rang the local Fiat dealership and they wanting £75 just to bring it into the garage to plug it in and diagnose the fault. A local independent garage said they would do the diagnostics for £30. But in the end I bought a cheap OBD-II reader from the internet for about £15 and found out what the fault was myself saving over £60 on the dealership costs. And bonus I still have the OBD-II reader I can use again in the future.
Apple aren't the first tech company to do this sort of thing, I remember from my days repairing HP/Compaq laptops the BIOS used to restrict them to working HP approved wireless cards and other manufacturers of notebooks use to restrict which optical drives would work in their laptops, for no good reason only than making you buy spares from them.