Hello Tose,
as the 7.2 release is quite young and Univention can/should only provide one version per app we decided to wait (at least) till the 7.2.1 release to iron out some potential issues in this mayor release before we force this update for all systems. (not everyone always wants to run the latest and greatest 
)
If you already want to run 7.2 anyway you can do the following (I do this on my test systems all the time):
- Install Zarafa though the app center to get the Zarafa fields into the Univention directory manager.
- download you desired Zarafa release from the Zarafa homepage and just update the packages via “dpkg -i”. Extra style points can be achieved for first putting the packages into a local apt repo and then updating by “apt-get dist-upgrade”.
Regards Felix
PS: Zarafa 7.1.12 and WebApp 2.0.2 should be available through the univention app center shortly. So you can at least have the latest WebApp if you decide for an App center only installation.