I'm not going to argue about sirloin, you're right on that. I prefer a rib-eye.
Luby's uses the same beef that those other places use, and the only way they'll cook it well done is if you're dumb enough to ask for it that way.
I don't want to rip Lubys in particular. Chili's or any other resturant like that usually has poor steaks. However these resturants do not use the same beef that Ruths Chris or Sullivans uses. True its beef and its not some strange form of beef, it just isn't the top of the line cuts that these other resturants use.
The Japanese Kobe beef feed their beef cows beer and even massage them. Many of the cows used at Ruths Chris are fed out for longer periods of time and use carmels and such in their feed.