Thanks for the link Thomas, but not exactly what I was looking for.
The Support Lifecycle of a software product is the period of time between when the software is released and when all support for it ends. Support generally includes bug fixes, security updates and email and telephone technical assistance. Eventually this all comes to an end, of course. Continuing to support all the iterations of a software product takes money and the ROI is less and less because fewer customers are using the older products.
Microsoft does a good job of spelling out their software support lifecycle. See this link as an example of what I am hoping to find from Apple:
http://support.microsoft.com/gp/lifepolicy