Why shouldn't they continually improve their products? Even with NTSC sets this was done. New ones would be larger, have better focus, more clearly resolve the signal, have better phosphors, and so on. Why shouldn't this continue? They should keep trying to improve their products as technology allows.
None of that means you need to buy a new toy all the time though. You can stick with what you have until it breaks, or until the new stuff is a big enough leap that you wish to own it.
I think a lot of the whining from people comes down to simple jealousy. They'd like to own the new stuff, but cannot afford it, or do not wish to. So they try and hate on it and act like a luddite. You see it practically any time Slashdot has a story on new technology. People complain about it like it is somehow a bad thing that there might be something new.