To be perfectly honest, In five years of working for INS, I have only seen one Immigration Lawyer who had a good grasp of Immigration Law.
Personally I don't trust immigration lawyers and do not recommend them to immigrants. There are many free or low cost services out there that know more about immigration law than most immigration lawyers.
Just my opinion and your lawyer may know what he is saying, but most immigration layers never went to school to study immigration. If you wish to know about immigration law, the best person to speak with is an Adjudicator or Inspector.