One source of early confusion was a widespread popular notion that only Cohens or only Jews could have the Cohen Modal Haplotype. It is now clear that this is not the case. The Cohen Modal Haplotype (CMH), whilst notably frequent amongst Cohens, is also far from unusual in the general populations of haplogroups J1 and J2 with no particular link to the Cohen ancestry. These haplogroups occur widely throughout the Middle East and beyond [8],[9]. So whilst many Cohens have haplotypes close to the CMH, a greater number of such haplotypes worldwide belong to people with no likely Cohen connection at all.
http://en.wikipedia.org/wiki/Y-chromosomal_Aaron#Responses
Or maybe the ancient Cohens simply got around to more households than were Jewish.
Know what I mean? *nudge, nudge,wink wink*