I can't say I've really seen an effect on crawling from supine sleep. OK, I was in med school when the recommendation was made but my patients crawl.
I do see the flat heads.
The phenomena fascinates and frustrates me.
Example, I walk into the exam room, baby is lying on the exam table supine, mom standing at the side of the table, dad sitting in a chair or not there. 
Parents say the baby is gassy, I tell them to hold the baby upright a lot so the gas rises to the top of the stomach and passes easily, maybe I even go on to explain the esophagus going into the posterior of the stomach, maybe even further I mention a freind who is an anthropologist and how she told me of baies in West Afirica without gas.
Parents copmplain the bay gets fussy, I respnd to hold the baby more
Parents complain the baby spits up, I say hold the bay upright a lot.
During my exam they comment on the baby's flat head, I say hold the baby more.
So after I'm done what do they do? They let the baby lay supine on the table !
I give up! I hand the baby to the parents. S/He is yours you made him/her you get to hold him/her.
Not suprising the breastfeeders tend to have rounder heads even though they too sleep supine.

Rob 

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