Hello Linux Geeksters. As you may know, Ubuntu Touch, the mobile version of the Ubuntu system, is developed on two branches right now, Ubuntu-RTM which receives less new features and more bug-fixes and ubuntu-devel, where all the changes get submitted.
While both the Ubuntu Touch branches should normally adopt the Ubuntu 15.04 system as code-base, the developers have decided to keep the RTM version utopic-based, so that it will be ready for usage on the Meizu phone, announced to be released with Ubuntu Touch.
Before releasing new Ubuntu Touch images, they have to pass a big number of automated tests. If the tests are not passed, the images do not get promoted.
For now, Ubuntu Touch is officially supported only on the Google Nexus 4 smartphone and the Google Nexus 7 2013 tablet. Also worth mentioning, Canonical has announced that Ubuntu Touch will be used by default on two phones, developed by Meizu and Bq.