@KoiwiGal - I think you are thinking too much about the kinds of glue they use. The epoxy might not be very strong at all.
Think about it in these terms. If you have painted a wall and then your teenage son decides to sticky tape some posters onto it, wouldn't you like to know that the paint isn't going to come away when he pulls them down?
Not to mention that this might also indicate other things, like how long it would take before the paint starts flaking, or various other things. I don't know, I'm not an expert, but people seem to be able to extrapolate from this kind of experiment.
At any rate, I'm sure that they conduct these kinds of tests for a reason, otherwise they wouldn't waste the money and time doing it.