Yes, not all homeowners care enough to properly maintain and repair their plaster walls. Some--in fact, the majority--just want the thing done, no matter how sloppy the work. So, you will find that your previous homeowner applied wallpaper to crumbling, cracking plaster walls chiefly as a method of holding the plaster together. The sad part of this is that it actually does work, to some degree. A few good layers of wallpaper over the years will keep the plaster hanging together. But eventually whatever is happening to the plaster will transfer to the wallpaper. So, plaster cracks will mirror themselves on the wallpaper. It's a short-term solution, and a lousy one at that.
Be careful before attempting to remove wallpaper from your old plaster and lath walls. The wallpaper may be holding together some horrors beneath. Be prepared for full-scale plaster repairs in the event of paper removal.