The real problem of the 1DsMIII for me lies in the lenses. I have a nice colection of Canon glass that performed beautifully with the first 1Ds. When I upgraded to the MII then some of them perfomed less well due to the increased resolution, with added work in my sharpening routines, which will only get more picky with the MIII. Now, what sense does it make for me to upgrade to the MIII if my lenses are not up to the job? It would be like crippling the sensor. And to be clear I only own L lenses, except for the 50 1.4, which incidentally performs better than most of them.
So I wouldn't buy just the body, but a full kit of probably Leica or Zeis glass especially on the wide side (which many people here swear are way better than Canon glass. I don't know since I've never tried them on my canons). Under that premise it isn't that cheap to jump into the high mpx count by just buying a DSLR like the 1DsMIII.
It's not just the lens, it's the aperture used. Photodo, famous for their now-discontinued MTF testing, explained that the reason they never took the trouble to test the lenses at f11 is because they found that all lenses are equally bad at f11.
Perhaps that's a slight exaggeration, but certainly less of an exaggeration at f16.
By using f16 for all cameras in this test, one is ensuring as far as possible that all the lenses are equal, so in a sense this is a perfectly valid test for that purpose, ie. how does the 1Ds3 compare with sensors double the size when the lenses used are equal?
One could do a similar comparison between the latest Olympus 4/3rds camera, the E-3, and the 1Ds or 5D. Using a Zuiko lens at f16 would rob the lens of its resolution advantage compared with 35mm lenses, an advantage which it actually needs because the sensor is smaller.
It's a matter of simple mathematics that the smaller sensor cannot compete with the larger sensor (of similar pixel count) unless the lenses used with the smaller sensor are better, that is, have a higher MTF response at the same spatial frequency.
Now the differences in format size between the Olympus 4/3rds format and 35mm is greater than the difference between 35mm and the P21, so one would expect any comparison between 35mm and the 4/3rds system at f16 to be even more disastrous for the 4/3rds system.