But then, is it accounting malpractice not to advise the client of the requirement to file and the penalties for not doing so?  And then just send them down the street to the friendly neighborhood lawyer?  (Or tell them to figure out how to do it themselves.)  

And there is no federal definition of the practice of law.  Each state has its own.  Do real estate agents practice law? In Arizona, we had to amend the constitution to let them stay in business.  The same was not done for tax return preparation, although it could have been.