Yes, that's the concept. Move the disk to a TV where there's no cable/aerial connectivity and a foreign TV. Actually, I have one of each - a DishTV DVR and a HTPC - the DishTV is where the aerial connection is and the HTPC is for the kids so we have better control of what content they watch.
The appliance has clear advantages as mentioned above, and the HTPC serves a different purpose. My view in brief:
Appliance: simple, easy to use, cheap, quiet, can be left on most of the time, just does TV
HTPC: complex, more expensive, can do more than just TV (skype, web browsing, music, photos) with a better interface for each, noisier (fans etc) than appliance
Each has its own use and considering the appliance is only $150 or so, it's a simple equation to put it where you just do TV. Of course if you have plenty of cash and time, a HTPC does make an awesome experience.
Add smart TVs to the equation and things get interesting... :)