As CDRT notes, here in the NorthEast, use of dots versus open are also about 60 / 40.
Mostly, those utilizing red dots seem to be the newer 2700 shooters (fewer and fewer each year) and older shooters. The new I think because of it being easier to sight with. It limits the need to really master the fundamentals of sight alignment, and concentrate more on trigger control. The older shooters use them mostly due to necessity, to keep shooting as eyesight begins to decline.
I switched to red dots around mid to late 80s. My bullseye scores went up, but did not do well in subsequent distinguished matches trying to achieve the gold. Went back to iron, (.45s with Bomar ribs) practiced more and got distinguised next four matches. I still shoot iron sights and still have Bomars on both my ball guns. (1 Clark, 1 Crawford)
It might also be a bit ironic that Don Hamilton set the National record for highest score at Camp Perry with open sights, and it is still a 30+ year record not yet broken. Also, the majority of those in the 2770 club were shot with open sights, but this is beginning to change.