You guys are right; I should not have spoken about Canon because I have no experience. But I do have a lot of experience with Epson and there, there is far more sensitivity to media type in the X900 generation. I started with Epson 2000 and 9500 machines. Then, we did not think about media setting except perhaps when a exotic paper proved too think. With the X800 generation, I printed alternately on paper and canvas without changing the media type setting on Imageprint 7, and rarely gave it any thought.
With my 9900, every non-epson media requires careful selection of the media setting and some media feed adjustment. You may not initially notice a problem with the setting when changing media type, but in my case, the problem surfaced in solid blacks and even other solid colors. I initially thought there was a problem with the black ink pump, so I called Epson. In contrast to the Canon users' experience, Epson only tested the printer with Epson media and declared that there was no problem. When I showed him my funky Museo canvas prints, the answer was: we do not support non-epson media. That was the end of my support case.
Since then, as I said, I have found that it is possible to find a setting that works with most third party media. But unless you are married to your favorite paper, it is just less hassle to find the equivalent Epson media that you like and get on with printing instead of constantly fiddling with media type setting and adjustments.
The Canon user that began this post said that Canon support initially asked him to try different settings and eventually suggested a similar Canon media that would not present the scratch problem. Sounded to me like a gentle nudge by Canon as opposed to Epson's brute force -- a matter of differing strategies while sharing the same anti-competitive impulse.