60d/7d suffers from softness caused by defraction

In an earlier post I mentioned this. I seen it on the Digital Picture site. I sent him an email and this is his response. My original post below that. From what I see his explanation appears to be the cause. I have never shot my 7d at F8 very often and tried to view 100 percent crops to test defraction but I will try it on some very sharp lenses to see.

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The softness you are seeing at f/8 across all the EF-S lenses is the effect
of DLA--or "diffraction limited aperture". For the Canon 60D, the DLA is
f/6.9. Using apertures above the DLA will result in a loss of sharpness (to
some degree) across all lenses (regardless of their individual performance
at any given aperture). If you check most of the lenses at f/5.6, the
results will likely be better than the f/3.5 and f/8 results.
The reason every EF-S lens looks a little soft at f/8 is because you can
only test EF-S lenses with crop sensor cameras (like the 60D). The crop
sensor cameras generally have a lower DLA than full frame cameras--for
example, the 5D Mark II's DLA is f/10.2 compared to the 60D's DLA of f/6.9
(meaning you'd have to be shooting at an aperture of f/11 with the 5D Mark
II before a loss of sharpness due to DLA is evident).

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While replying to another thread, I was going to give examples how a lens could be soft at f wide open and sharp at F8 on a 60d.

So I head over to the digital picture where the guy rates lenses and shows us how they differ in resolution at different focal lengths and fstops. So I go to there for a view of the EF-s 18-135 on the 60d.

What I find there is no difference in apparent center sharpness between wide open and f8 at any focal lengths.. they all look very soft.

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=809&Camera=736&Sample=0&FLI=3&API=3&LensComp=0&CameraComp=0&SampleComp=0&FLIComp=0&APIComp=0

So then I look at all the other EF-S lenses, the ISO test shots are all taken on the 50d 15mp or the 60d 18 mp. They all exhibit the same behavior all soft. You can see the images change slightly and when choosing f16 you can see the images get a little softer or show CA.

So then I checked all the EF lenses and you can see a difference between wide open and stopped down, except for primes 135 and up seen to not get sharper as you get to F8. They are sharp all the way.

So then I look at DPreview of the EF-s lenses there are tested on the 450d which has a 12mp sensor and it shows that there are differences between center resolution at different Fstops.