https://www.google.com/search?q=average+US+row+width+for+soybeans&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7ADRA_enUS421

I tried to find it in a quick search but didn't.

I don't agree a majority is 30 inch, I am thinking at least half are 15 inch or less.  30 inch rows were rare in my 10,000 mile scouting trips this summer.

I do agree corn is bred for 30 inches as I have talked to breeders but a few are working on narrower row width breeding.

Ed