I've ever fixed a Dell desktop before many years ago, one running an AMD Phenom II, and its true that some of the parts are proprietary. The motherboard then was fortunately a proper ATX format and I think it was the same cooler used as shown in this video, apart from the mount being different.
But truth to be told, I feel the weird/ proprietary components used in these OEM systems should not come as a surprise. Tech savvy folks usually stay far away from these systems either due to cost, inflexible specs, and opaque components used. I was considering whether to get an Aurora 12 earlier, but decided the casing looks too restrictive and cooling for the components looks subpar. To perhaps 90% of the population, the system works, i.e. don't lag, or freeze, and that's good enough. As to the hidden warranty charge, I think that is a problem and people should always check the specs and charges before making payment.