Percona Software in Ubuntu 14.04 LTS (Trusty Tahr)

If you install Ubuntu 14.04 and run aptitude search you will find:

Percona Toolkit and Percona XtraBackup are up to the latest versions, but Percona Server and Percona XtraDB Cluster comes with 5.5 versions, and it is in line with default MySQL version, which again is 5.5