Not all updates for CRM 2015 are available for all components. In particular the Update 1.0 series (which introduced functional changes) is not available for On-Premises server. However, Update 1.x is available for some of the other components.
Note that even though the Microsoft KB article references CRM Online in Update 1.0, you can still apply Update 1.0 (and later) to the CRM for Outlook Client if connected to an On-Premises server.
Click on the Update heading to navigate to the Microsoft KB article for the update where you will find a description of the build, bugs fixed and a link to the download.
Given the anticipated release of CRM 2016 before the end of 2015, I don’t expect we will see an Update 2.0 release for CRM 2015.