Windows Media Center is infected with "Macrovision." Macrovision is the crippleware that some TV stations and networks use to stop you from recording their shows. Though there is no law requiring manufacturers to install this kind of Macrovision — and though it's not illegal to ignore Macrovision and record a show anyway — Microsoft implements it for WMC, and infected its customers with it after disguising it as an "update."
Microsoft probably did this to bribe the cable operators into giving it access to encrypted television, though it's possible (and legal) to record their shows without permission by using the analog outputs (like the Neuros OSD and mythtv, a DIY Linux-based recorder).
