I've been wondering why canonical releases a *.04 release (ubuntu), advertises that it is supported for three years, and then a *.10 release comes out and isn't supported for three years.
My question: what's different about the *.10 release?
Canonical has Long Term Support releases that are supported for three years on the desktop and 5 years on servers. These are released every two years on even numbered April releases. (So your comment about April releases is only half right. For example, 9.04 wasn't an LTS release but 10.04 was).
Canonical does this to ensure that people will have support (security fixes, backported drivers, etc) of their operating system for a long period of time, while enabling Canonical to have major releases on a comparatively fast and regular schedule. (There aren't many other operating systems that put out releases every six months).
It's great for server admins as well as large adopters of the system because they don't need to upgrade as frequently and they have a long term upgrade schedule ahead of time.
Note: from 12.04LTS, the LTS-versions are supported for 5 years
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