Originally posted by RKKS08 My impression, too.
Possible reasons?
I don't know for sure, but I have noticed that they all seem to be issues with distant subjects. I wonder how many of these folk live in areas with poor air quality, persistent haze, or temperature-related atmospheric distortion. Here in the Pacific Northwest the quality of our landscape photography is often limited by moisture in the air. It wasn't long after I got my K10D that I realized that the more air between me and my subject, the less likely it was that I was going to get a crisp photo.
While it is possible that the lenses in question are not properly collimated for infinity focus, it is more likely (in my opinion) that the fault lies with atmospheric conditions, choice of subject, flare, camera motion, fungus, or any number of things that can contribute to image softness. It might also be that the lens is really not that sharp to begin with.
Steve