A corporation, being a legal fiction, can only act through physical persons. So in that respect, no corporation can be truly autonomous. It sounds like what they have done is taken all the paperwork associated with corporate activity: by-laws, annual meeting minutes, resolutions, etc., and put them into a block chain. A more proper description would be a paperless corporation.
Just the fact that people put their money together and are acting as a group gives them various legal requirements. The fact that the DAO limits what they can do might interfere with their ability to follow the laws; that does not mean that the laws do not apply. You don't get to throw your hands in the air and say "we cannot pay taxes on our profits, it's physically impossible" when you made it impossible yourself by creating and/or associating with the DAO.