One of the great things about the double-barrel open source software and fee-based subscription support strategy that commercial Linuxes have is that there is very little economic pressure on Linux shops to upgrade from one version of the platform to another as their Linux vendor (or vendors) tweak, change, upgrade, and improve their distros. They get to move when they feel like it, and vendors who want to keep their customers agree to support their older releases for a long, long time.