One other consideration for in-body SR vs in-lens IS is the
following: with in-body SR, if you upgrade the body to one with a
better SR system, you automatically upgrade the stabilization on all
your lenses. The down-side, as mentioned, is that if the in-body SR
goes down then you lose SR for all lenses.
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At this point that's highly theoretical re the Pentax lines. They carry forward existing componentry all the time, and the K20D is very much the K10D, by their own admission, while the K200D represents an upgrade of the K100D.
Each ends up with a step-up in sensor from their respective ancestor, on that basis (and the naming convention), with the K200D getting the K10D sensor, and to their credit, improving the JPEG rendition in the process.
Canon and Nikon have not had to improve (or risk loss of performance) on new bodies, because IS in the body is NOT a consideration for them. They can create each lens as a total unit, with IS and AF included, with motors designed for each class of lens - short, medium, long. That leaves room within the body for more features.
Since Samsung is openly pushing towards an FF system, while Pentax instead got hung up with the 645D, likely we'll see an entirely new body when FF comes about - and in order to compete in THAT market, the in-body IS will become a liability vs. the competition. Right now, it's probably of some marketing advantage since the lens is reduced in cost; but the manufacturing and component cost of the body's added complexity may offset that due to their comparatively low production volumes vs. the competition; generating a higher overhead cost per unit produced. While the mass-production lens factories are in Vietnam, I understand that some of the "better" lenses are still made in Japan.
As to your perceptive:
"The down-side, as mentioned, is that if the in-body SR goes down then you lose SR for all lenses."
A pro would rather substitute a lens than lose a body, what with the overlapping ranges of zooms available as to perspective. Pentax, to their credit, seems to have kept the moving parts of the system simple; but it sets up an operational dependency for the IS, against each individual lens. This is where a long tele becomes the exception, as vibration can send its image further off-axis.
In terms of front/back focus, Pentax has an entire system within the K20D attending to that problem BY LENS.
http://theonlinephotographer.blogspot.com/2006/12/more-on-in-camera-vs-in-lens-image.html
(from back in 2006)
"Some of Canon’s competitors have chosen to use in-body image stabilization. The technique involves moving the image sensor in a controlled fashion, based on signals from movement detecting sensors in the camera body. The obvious advantage of this system is that users have some sort of stabilization available with almost any lens they connect to the body. Short focal length lenses require smaller sensor deflections; 24 or 28 mm lenses might need only 1 mm or so. Longer lenses necessitate much greater movement; 300 mm lenses would have to move the sensor about 5.5 mm (nearly 1/4”) to achieve the correction Canon gets with its IS system at the same focal length. This degree of sensor movement is beyond the range of current technology. Short and 'normal' focal length lenses need stabilization much less often than long lenses, so the lenses that need the most help get the least."
(I have no idea of what the deflection range is of the current Pentax IS system. I do know that the image circle of the made-for-digital lenses is quite tight to the APS-C sensor; whereas for 35mm film you could have some "slop" without a problem - for example using the Pentacon-6 Zeiss MF lenses on a Spotmatic)
