This is just my own personal experience as a person who has lived in Kansas most of her life!  The local farmers who grass-feed make it a point to let you know that they eat nothing else, strictly what nature provides in the pastures.  (I live in Hutchinson, which is about 40 miles northwest of Wichita.)  Out west, in the Dodge City area where most of the feedlots are, there is never any grass to be seen, at least not when I have been by there!  It's just dirt and pens for miles.  (In the feedlot areas, I mean...there IS grass elsewhere in western Kansas, ha, although not much!)  
 
Now, if the grass-feeding farmers finish-off with grain to sell to a commercial entity, that I do not know...I guess I need to find out!  But the ones where you have to go to their farm to buy, they don't do that.  
 
Love,
Bren


 

AFAIK there are no feedlots in my area, but many farmers. All but two of them sell grass fed beef which is traditionally finished on corn.
That corn is said to be marked "Unfit for Human Consumption", I suppose because it is genetically modified and therefore contains unacceptable levels of pesticide/biological poisons, as well as the problems caused by eating GM stuff.
I found one who has buffalo. She said she give them some grain as a treat! I've never heard of a farmer who treats their livestock as pets.

So "grass fed" is a marketing ploy intended to make us think that we are getting what we need.
It's the sellers who are being humorous.   After all, they think we're nuts.

William

"You are what you eat"