So, basically - There's new updates occasionally with what appears to be bug fixes. It sounds like October every year Xara/Magix releases a new title with new features. We can pay half off the software for the new version if you're an existing customer.
A user on TalkGraphics (message #72) indicated that he has 17.0.0.58775 dated March 17. It's possible that the notes were made before the update came out, then the patch was checked and modified with a new build) and no one thought to update the notes.
Yes, Xara issues new features about 2-3 times per year and a new version once a year. Intermediate bug patches are also issued.
I suggest that you hold off renewing until you see some new features come out that you would like to have or if you are caught having to reinstall Xara WDP and the best that you can get is an older version. See the details of the Update Service, especially the long version on the TG forum. I presume that you downloaded all of the on-line catalogue content before your Update Service period expired.