In general digital bits burn out and have shelf-life. The digital world is not nearly as eco-friendly as some may say it is!
Hard drives only last about 3 years. Greenboard solder connections have a defined life, as do capacitors and silicon chips. And, when they go, most people (even handy people) can't just replace them, like you could with a winding mechanism, for instance, in an SLR.
If you were enterprising enough, you could often adapt an antique analogue system for some kind of current use. My brother and I even played with old movies by putting our own light source and magnifying glass, to see the images on a wall where we didn't have a projector (no audio, though, and not exactly 24fps). With digital, if your system doesn't support some kind of format, then you are out of luck. This, by the way, is one reason I hate focus-by-wire. Those lenses will be worthless when the bodies stop supporting their format. At least with (e.g.) EOS lenses you can still focus, and with even older lenses (FD, OM, Takumar), you have on-lens Ap control. Manual, yes, but fully functional.
In the analogue world, "close enough" could sometimes get you buy. In the digital world, precision is key. Take for instance television. In the analogue world, a coat hanger jammed in your broken antenna could get you a snowy picture, but it would at least be something. In the digital world, you might not get enough data to assemble any picture, or you'll get a lot of cut outs and jerky shots.
There's a lot of things going for the digital world, but reuse and stretching the life of a product are not the strong suit. Use it and toss it. That's why moving on to the "next new thing" is actually kind of important. It seems to me camera values start high initially, plateau out for a while, and then drop to zero because the unit ceases functioning. It's also why I don't think cameras like my EP1 are going to be "collector pieces" -- the circuit board will eventually die, and it will be useless. Unlike perhaps an old Canon rangefinder.