Do you mean real IBM cases or some IBM compatible cases?  I've never seen a real IBM with that kind of a case.  Years ago I had dealings with Apple at multiple different levels.  At one point it was necessary for John Sculley, who was at Apple at that time, to use a PC system.  They asked repeatedly if it was possible to port the application to a Mac, but there was simply no way to do it, economically or time-wise.  So the solution to avoid hurting Apple's pride was that I was given an Apple badge to place over the IBM badge for as long as the equipment was being used by Apple.