His photo raises the same problems as were raised in the Eggleston discussions we had on APUG in the Discuss a **** photo forum. I don't think one should laugh at people not "getting it" the same way one shouldn't see things only technically and by-the-book-rules.
For my part, when I saw people laughing their head off at others not "getting it" I thought there was some kind of inside or subtle joke in his picture (e.g. you have to look at it in a certain way and suddenly a dirty thing appears, etc.). I didn't "get it" for a long time, and eventually figured out that the photo works out of the tension between the flat surrounding colors and the "angel picture" the woman is holding. But I could hardly blame people for missing that.