I've never had that issue with roundup on bermuda. it turns brown where I spray it. hold it close to the ground when you spray. it may go slightly more but not several feet. I can spray around a post and it will make a few inches of brown around the post and that is all.
cracks in driveways and weeds in flower beds are the main things I use it for.
most guys on lawnsite mow smaller yards where there isn't a lot of trimming needed so there is no use for roundup. when you are mowing 4 acre yards it is almost necessary. you can't make any money if you are spending over an hr trimming a property. they just aren't going to pay you that much.
there are also many places where you can't even use a trimmer if you wanted to.
behind and a/c unit next to a house with hoses running under the house and you can't even fit a trimmer head back in there.
under a deck on the back of the house that is only a few feet off the ground. you just can't get a trimmer under there to do anything.
brick patios and sidewalks where weeds are growing up between almost every single brick.
roundup use is unavoidable in these situations.
I guess other areas don't deal with this type of thing. I see something like this on almost every single yard I mow. I can't just leave it and let it grow up like a jungle. it has to be taken care of.