UPDATE: This article is out of date - please refer to: Joomla Extends Releases to Two Years
Here's an interesting article that was just released about the Joomla development path:
How upcoming changes may affect your Joomla upgrade schedule (anything-digital.com)
Many site builders have expressed frustration that 18 months was too short a window to realistically expect sites to be updated, especially for client work.
The good news is that it sounds like each major version (LTS / Long Term Support) will be extended by 6 months. They're showing Joomla 2.5 being supported into 2015 instead of just 2014.
I think the confusing thing with this path is that the major versions are the x.5 versions instead of the normal, x.0 versions. That's creating some confusion out there for sure. People see Joomla 3.0 come out and wonder if they need to upgrade since it sounds like a major release.
Let us know if you have any questions.