So how is that DRM free?
It is not. You can purchase the song; but you cannot copy/publish/give away, etc.
FWIW, DRM stands for "digital rights management" which can also mean "copyrighted" and most CDs or DVDs are now coded so as not to allow someone to copy it. Whether you buy a digital version or on a CD makes no difference - you are not allowed to do anything but listen to or watch it. Here is an excerpt of the Terms:
INTELLECTUAL PROPERTY
You agree that the Services, including but not limited to Content, graphics, user interface, audio clips, video clips, editorial content, and the scripts and software used to implement the Services, contain proprietary information and material that is owned by Apple and/or its licensors, and is protected by applicable intellectual property and other laws, including but not limited to copyright. You agree that you will not use such proprietary information or materials in any way whatsoever except for use of the Services for personal, noncommercial uses in compliance with this Agreement. No portion of the Services may be reproduced in any form or by any means, except as expressly permitted by this Agreement. You agree not to modify, rent, loan, sell, or distribute the Services or Content in any manner, and you shall not exploit the Services in any manner not expressly authorized.
From here:
Legal - Apple Media Services - Apple