See, IMO, I don't really understand this idea either. IMO, "off-screen" events are not part of the actual game, since they are not adjudicated by the rules (well I guess they could be, but I don't know any DMs who actually do this), they're part of the larger narrative that encompasses the game and are essentially subject to DM fiat.
Some people look at how the varying super beings in 3e were statted and would object if Asmodeus tooled Kurtulmak in a straight-up fight off-screen because this could never possibly happen on-screen if their stats were used.
In other words, in 3e, it was generally assumed that stats were objective statements about the things so statted, whereas in 4e it's assumed the same being may have completely different stats if encountered alone, in a group of five, or in a group of twenty. (And no meaningful stats whatsoever beyond "what the DM thinks" if it's encountering people who aren't the PCs.)