I have to agree with Jason here. Not every repaint we do is for the single guy driving the Porsche. Some people just cannot afford or do not want removal of (sometimes multiple layers) of wallpaper. This can get very pricey. Don't get me wrong, I've done a lot of jobs where stripping the wallpaper and repairing/priming the drywall underneath is done. I agree this is the "proper" way to do it. However, sometimes that's just not what the customer is willing to pay for.
When we bid a repaint for a room with paper, we tell the customer what should be done. We explain that the wallpaper should be removed, etc, etc. Then we give them the other option, paint over it! We have done a number of jobs where we simply skim the seams then prime and paint right over top of it! The customer knows before hand that there is no warranty, and it (generally) will not look as good as removing the paper. Some people just want to get the color on the wall.
Is it the right way? probably not. Is it what the customer is willing to pay for? Yep. Will I walk away if the customer wants to pay me to do it the cheap way? Nope!