Technology getting cheaper by the second ...

I'm amazed. A friend has just sold me a television that he said he bought about five years ago for around £3,000. It's a plasma panasonic something or other. He did bring around all the bits of paper to go with it but I can't find them now! Anyway, my point is he sold it to me for £200. That's amazing isn't it? Why on earth do televisions lose their value so quickly. Is technology really so fast that everything becomes redundant that quickly? Should I not bother buying anything ever as it's just going to lose value by tomorrow???