Definition of user agent?

Colleagues,

What is the significance of the addition of this sentence to the definition of user agent:

This standard applies to user agents that (1) can access the general browsable Web; (2) have a user
interface that satisfies the requirements in Determining User Preference in the [TRACKING-DNT] specification; (3)
and can implement all of the [TRACKING-DNT] specification, including the mechanisms for communicating a
tracking status, and the user-granted exception mechanism.

Does this mean a user agent is not compliant if it doesn't implement the UGE mechanism?

Regards,
John