Ok to sum if up then:
1. Usually, but not confirmed, an os becomes obsolete after 3 later versions are released. That would mean when ios8 is out, then 5 is obsolete.
2. However, this is based on the Mac OS model. Unconfirmed, but probable.
Add questions and responses:
Support definition: I meant in terms of calling someone to troubleshoot a problem. For example, I have a Mac that is 15 years old running some os I can't remember. If I call for help, they will say "dude, we don't support that product anymore"
In regards to your response, my original mission was to find something on the apple.com that states an official policy like this. I can't find anything. Nor does it seem like an apple rep can confirm.
Also after reading this article, I suspect it's just not apples policy to release an end of life roadmap for iOS.
http://www.zdnet.com/blog/hardware/does-apple-need-to-publish-an-end-of-life-roa dmap-for-ios-devices/12643