TBH, I don't mind my meat to be a bit tough, if it is tough in the right way. Flank steak is always going to be flank steak, and I'm not a fan of those tough threads of sinew. But, I don't mind at all if my sirloin has a bit more chew. Grass or corn fed, sirloin isn't going to get strings of stuff stuck between my teeth.
The most tender parts of the cow are often what are referred to as "reactionary" muscles. These are the parts of the animal that aren't used all the time and are therefore more tender. A great example of this is the "hanging tender", which is a muscle that's just kind of... there. It serves no function and because of this, damn does it make for some good eats. http://www.smartkitchen.com/resources/hanging-tender So, the trade off is that cows that are treated like shit all there lives will likely be more tender because they've rarely been allowed to move.