Oh, the motion interpolation thing is because stores are constantly running their HDTVs in Game Mode, because their biggest customers are sport enthusiasts. Basically, whenever a sporting event (or video game, or rendered movie) is playing, the thing looks *exceptionally* smooth. Live TV and movies, not so much. I think the big chain shops are smartening up about this a little which is why all of a sudden they all seem to be huge Dreamworks fans, and why Monsters vs. Aliens suddenly has a framerate that would Yuji Naka pop his monocle.
It works the same way at home: if your TV has a Game Mode, make sure you turn that off once you stop playing games. Which you probably want to anyway since most TVs that aren't optimized for that tend to drop the picture quality to compensate for the extra processing demand.