Another issue for those of us that became photographers in the analogue age is that back then the body didn't matter too much. It was simply a housing for the shutter and film, that allowed us to hang a lens on the front, and provided a reflex viewfinder (if we are limiting ourselves to considering 35mm SLRs). As long as you could easily wind the film, and cock the shutter, set the required shutter speed and load the film, the exact body didn't really matter too much. The lenses were important, as was choosing the most suitable film stock for the task envisioned.
As the ability to integrate electronics into camera bodies improved, then so did the differentiation of camera bodies. Better internal metering systems, and the ability to use the meter readings to set either the aperture or shutter speed, based on the previously set other variable, along with the speed of the film. Of course this also then developed into the ability to set BOTH shutter and aperture with the introduction of program modes. At the same time flash guns (as we used to call them) developed and initially used internal metering to measure the flash output, and eventually the camera's metering system to provide TTL flash metering. Although all of this technology made things simpler for the photographer, none of them seriously changed the fundamentals of what a camera did, and the lens and the film stock was still the ultimate arbiter of image quality. Even the introduction of the Minolta Dynax and in body AF systems didn't make a really significant change to the QUALITY of photographs, that was still down to the lens and the film. You could take a basic SLR, or the top of the range model. If you used the same settings, the same film stock, and of course the same lens then the results would be identical. You never HAD to upgrade the camera body to get better results, as you could always use the better lenses, and the latest film stocks in the body you already had. The differentiations in the bodies were much more to do with convenience and easy of use, not ultimately image quality.
Of course with the advent of electronic sensors, and ultimately the the spatially as well as tonally digitised, digital sensors we use in today's cameras, the choice of camera body took on a whole new importance. Now it seems that the manufacturers are able to segmentize the market not just by convenience factors in bodies as was the case previously, when improvements in film emulsions could be utilised in any existing camera body, but also by pretty fundamental differences in overall image quality thanks to the fixed digital sensor in each camera. So now if you want the latest in sensor technology you may well have to buy a body with many features that you don't actually really need, simply because the advances in one specific area you do need are not available.
It would be really nice to see one of the major manufacturers produce a DSLR with an interchangeable sensor module. In many cases what we want to upgrade is our modern equivalent of film, the sensor. Being able to upgrade your sensor at a reasonable cost would be great, especially if that also lead to the development of specialist units. Monochrome, or high resolution units would become options as they are likely to appeal to many shooters, who wouldn't go and get a dedicated body for such features. If the manufacturer made the units with a consistent electronic interface you could then have the option to upgrade the body with it's AF, metering and flash systems as technology advances, as well as keeping the old "body" and picking up a new sensor as one comes available. Or even keep your old but liked sensor to use with the latest body systems.
The above though is I think unlikely, I'm sure that for the camera manufacturers (if not for the poor retailer who has to stock ALL of the models) that having a very segmented market for a quickly obsolescent product is a much better business proposition.
Alan
