Just the domain itself. IMHO, if I purchase exampledomain.com I should be able to point that domain anywhere I want, to say IP 66.81.153.87 (random ip). To me, that is the function of a registrar, to associate exampledomain.com w/ an IP addy. NOT to say 'ok you are the proud owner of exampledomain.com, now buy a hosting package' This is the first time I have run across a registrar that does not give you control of the DNS entries for the domain you purchased.
To give an example. Say I owned a business and I get Cox business internet service. That comes w/ a static IP. That static ip is say 68.91.65.125. This company has their own web server, email server, etc. Now if I go out and purchase Myownbusiness.com, w/ the purchase of that domain alone I should be able to point myownbusiness.com to IP 68.91.65.125. What good would a hosting package do me in such a situation?