My take...a TV does basically one thing at a time...it provides an image whether static or moving. Even the el-cheapo flat screens of today can be made to look very, very good. Comparing what a TV does to a car, or a cell phone is not apples-to-apples but rather apples-to-oranges. A car does more than just drive you from place to place. It also does all sorts of navigation, music playback, and even video playback as well as many more things too numerous to mention here. As for a cell/smart phone...well we all know what they are capable of.
Now if all cars only drove you from place to place and nothing more then I am sure they would go down in price just like TV's. The same could be said about cell phones. If all they were capable of doing was making a phone call and nothing more...they too would become blasé and the prices would fall to stagnation levels. YMMV