A good source of basic statistics and legal advice about nursing home abuse is the National Center on Elder Abuse at http://www.elderabusecenter.org/. It offers a wide variety of information on how to detect elder abuse, and should be one of the first places you go if you think a loved one has been a victim.
You'll hear a number of excuses for nursing home abuse: staff burnout, overwork, staffing cuts, and the like. While they may all be contributors, it's still the responsibility of the facility to take care of your loved one, and you should never just let the matter drop if you think a loved one has been abused.