There are at least two different questions in this thread.
One is whether the 20D is suitable for submission to various places, and the answer seem to be "yes" for some stock agencies, and some magazines such as National Geographic, but "no" in the case of Arizona Highways and some other stock agencies.
The other question is the one I was commenting on: whether the article by the editor of Arizona Highways articulates a rational basis for their policy of considering transparencies only, and in particular no digital images. For the reasons I stated previously, the answer there is another "no".
Finally, when someone publishes a lengthy argument in support of a decision he has been involved in, and that argument is obviously, fundamentally flawed, my hunch is that he in fact has no rational basis. Notwithstanding any legal right to make irrational decisions.