I can tell you that most of this is due to the developers themselves trying to cut corners, contractors that don't know/are bad at their job, horrible (city/building official) oversight of construction quality, methods, etc.  Here are a few of the things we have found in the building I live in (built ~2002).
1. Plumbing drains (for H20 heater emergency pressure relief) which stop 4' above the floor/connected to anything (so when a H20 heater relieved pressure it flooded the floor below).
2. Exterior vapor barrier which was put on incorrectly (so that water could not drain, instead damaging the building structure).
3. Windows which were too large for the openings, but forced in anyway (also incorrect flashing, caulking of drainage holes, etc.)
4. Structural reinforcement (in the approved/engineered plans) not built/overall building not built to the approved plan (still approved by the city/inspector).
5. Failed to paint a portion of the exterior (so the warranty is invalid).