Be sure to keep in mind chances are you will only see complaints posted in the various RV related Forums. It's rare to see someone post when they are completely satisfied with a system or RV.
Of the millions of RV owners these RV forums are only a small sampling. I doubt if the majority of RV owners read the forums and even fewer actually post in the forums. So it may seem as if certain systems, RV manufacturers or models of RVs have lots of problems.
We have had numerous RVs from various manufacturers from a camper shell (cap), MHs, TTs and our current 5th wheel. Most were brand new and each had their share of initial problems due to poor quality control and most had problems throughout the years of use that I would classify as due to wear and tear. I can't think of any problems that were due to early unexpected failure.
Also some failures may be attributable to user error. For example one RV'er had an engine in his tow vehicle go bad early. It turned out that he had over revved it coming down a long grade because he hadn't used proper braking/hill descent techniques towing his very heavy 5th wheel. The engine was replaced under warranty and he had an exhaust brake added to make sure it wouldn't happen again.