I think it looks like the rsync repo is out of date compared to the http mirror?
# curl -s http://repo.percona.com/centos/6/os/x86_64/ | grep "percona-xtrabackup-2\.2\."
<a href="percona-xtrabackup-2.2.3-4982.el6.x86_64.rpm">percona-xtrabackup-2.2.3-4982.el6.x86_64.rpm</a> 12-Jun-2014 13:38 4341548
<a href="percona-xtrabackup-2.2.4-5004.el6.x86_64.rpm">percona-xtrabackup-2.2.4-5004.el6.x86_64.rpm</a> 11-Sep-2014 10:33 4283300
<a href="percona-xtrabackup-2.2.5-5027.el6.x86_64.rpm">percona-xtrabackup-2.2.5-5027.el6.x86_64.rpm</a> 26-Sep-2014 09:17 4861680
<a href="percona-xtrabackup-2.2.6-5042.el6.x86_64.rpm">percona-xtrabackup-2.2.6-5042.el6.x86_64.rpm</a> 29-Oct-2014 08:27 4863040
<a href="percona-xtrabackup-2.2.7-5050.el6.x86_64.rpm">percona-xtrabackup-2.2.7-5050.el6.x86_64.rpm</a> 04-Dec-2014 14:18 4863276
# rsync -avn rsync://rsync.percona.com/rsync/release/6/RPMS/x86_64 /tmp/ | grep "percona-xtrabackup-2\.2\."
x86_64/percona-xtrabackup-2.2.3-4982.el6.x86_64.rpm
x86_64/percona-xtrabackup-2.2.4-5004.el6.x86_64.rpm
x86_64/percona-xtrabackup-2.2.5-5027.el6.x86_64.rpm
x86_64/percona-xtrabackup-2.2.6-5042.el6.x86_64.rpm