Looking at the release page, I noticed the short life of 13.04. It is only 8 months : April 2013 to January 2014.
Why is the life of 13.04 so short?
Canonical switched to a 9 month support plan for non LTS releases because back-porting bugs and package upgrades was consuming too much time for the company, since most users of non-LTS releases upgrade each cycle.
Source: Too much time wasted reading about Linux.
After further browsing, I found this :
The first link tells :