I don't like it either. In my first house, the people before me had put wallpaper up over wallpaper. That was a bitch to take down.
Ooh... wall paper over wallpaper eh?
The problem is that because it is a pain in th eass to put up, its expensive to hire people to do it, much less find someone who will do a good job... so they don't use sizng and all that crap... or they use border paste to put it all up. One of my relatives (by marriage

) actually didn't realize that her wallpaper was prepasted.
Another (huge) problem is that your average drywall/sheet rock is not a good base for wallpaper, compared to real plaster.
Anyway... My mom lives in a house that was built during/just after the civil war... worst room in there had at least 7 layers of wall covering that we could identify. (5 wallpaper and 2 paint). And there were probably more paint layers than that. Cool thing was that the people who put up the first layer had written their names and strange messages on the walls from the 1890's. (Apparently they had taken down the original...)
Anyway... done right... wallpaper can look better than any paint... but of course, as with most things, people are idiots.
My annoying story is that my house has a small-- almost useless-- addition that they finished in cheap wood paneling... then decided that was crappy so they put wall liner over that and then put some BS blueflowery shit wallpaper on top of the paneling.... so... I was moving in and had exaclty 2 days to fix this problem.... so it was either, leave it as it was-- not an option. Start ripping paneling out and put sheet rock back in-- not in two days. Or prime it and wallpaper over it. Which is what I did. Seems like the easy way out... but in the end, I'm happy with it, because it looks good (for now) and when I put an addition on my house-- hopefully next year-- this area will be demo'd. So I'm glad I didn't spend a zillion years messing with it.