What are the sales numbers for the 5Diii and D800 and the total sales of DSLRs for each? I was looking around a bit and couldn't find them.
Don't know about the sales figures...but approached from the other end: our content management buys about 3 times as many shot from medium frames then from D800's.And those in turn get outnumbered about 1:2 by each 5D3,5D2 and the other 18,24MP,whatever-cameras lumped together.
Partially because of the number of users, partially because its hard to get an actual advantage from the D800.
Sure, you have those islands of opportunity, but they are few and far inbetween - the 5D3 is a jack of all trades without real world weakness and if you're willing to retain a one trick pony then the MFs do that trick better.