It's marketing - make it seem not as good as the "pro" models and some people will fork out extra money on extra features most don't actually need. So they sell more.
Where-as the ones who choose the 6D know what they want and get what they want.
Then there's those who fork out extra for the 6D as opposed to the 60D.
Then there's those who choose the 7D for its "pro-like" features as it's the highest model of it's kind (APS-C sensor).
I could not be more happy with my 6D, everything works so perfectly! I just need a faster and bigger card for it - my old 2gb card I used for my compact camera only holds 38 RAW files
AND WHY WONT THIS FORUM FORMAT MY PIECE OF PROSE WITH THE SPACES I PUT THERE? :/