Is it that there is special TV-specific hardware like tuners, HW accelerated audio and video decoders, and PQ/AQ accelerators?

Apple has adapter their A15 chipsets for use in the Apple TV, so it seems possible. But obviously the Apple TV products don't have tuners, aren't driving a display natively, and probably don't have enough I/O interfaces to add all the extra hardware you'd need to embed it in a panel or STB.