Ubuntu 13.10 shipped with Qt 5.0 instead of Qt 5.1, since while it was available for months prior there were some "unfixed regressions" in the newer tool-kit release. With Qt 5.2 being right around the corner, Canonical is looking to switch to the newer open-source tool-kit release if there isn't as much fallout...
November 20, 2013
Ubuntu 14.04 Looks Toward Qt 5.2, Qt Mir In 14.10
Read more at Phoronix