I have to agree that not everyone needs to comment on every quilt. Just saying "nicely done" doesn't indicate that the viewer gave any thought to the quilt (but it is a way of increasing their post count on the board). It takes time to frame a thoughtful response. Plus, we all have our preferences and are drawn to different colors, styles, and designs, and commenting on something that just doesn't float your boat seems a little phony.
When I see that many people viewed but didn't comment on one of my posts it doesn't bother me. It doesn't mean they didn't like the quilt (although I'm sure that some did, and some didn't).
However, I do agree that when we see a quilt that really catches our eye, we should make an effort to let the quilter know that we like that quilt and why. But sometimes personal reasons get in the way of posting, and sometimes we just get out of the habit.