I know personally of a couple of cases where it actually occurred. Also, I have read several articles on the subject. An internet example can be found at http://www.fresh-eggs-daily.com/2013/07/the-real-scoop-on-using-sand-in-your.html
Thanks for posting a link to this info. It seems to be another all too common case on this website of people posting opinions without telling the whole story. Chickens who get an impacted crop are young chicks. They mistake the sand for feed and eat it. This doesn't mean adult chickens suffer from the same issue. Adding this to your post may be helpful instead of just cherry picking a fact to support your opinion while ignoring the whole story.
Frankly I'm getting a bit tired of this forum as people who have chickens for 2 months are suddenly experts in all things chicken. I would rather have no information than a forum full of misinformation.
Please don't completely misunderstand me either. There are enough people on here that are experts and do know what they are talking about. The problem is wading through the opinions to get to people who have practical knowledge.
Alex