I think the OP is being a bit naïve if they expect all users to upgrade to a new OS every year. Upgrades of Ubuntu and OSX are usually quite painful endeavours, fraught with UI-breakage and new bugs to solve, and there's usually little incentive for users to upgrade in every 6-monthly release.
IMHO Ubuntu has a good two-pronged approach - short-term support for most releases, but a LTS every couple of years for those who don't want to handle the pain of upgrading all the time.
Anecdotally, even upgrading to stay up-to-date with the LTS versions can be difficult. A company I deal with is currently scrambling to ditch Ubuntu 10.04 before it loses support in April this year. That's 5 years old now. Companies don't upgrade for fun.
I think the OP is being a bit naïve if they expect all users to upgrade to a new OS every year. Upgrades of Ubuntu and OSX are usually quite painful endeavours, fraught with UI-breakage and new bugs to solve, and there's usually little incentive for users to upgrade in every 6-monthly release.
IMHO Ubuntu has a good two-pronged approach - short-term support for most releases, but a LTS every couple of years for those who don't want to handle the pain of upgrading all the time.
Anecdotally, even upgrading to stay up-to-date with the LTS versions can be difficult. A company I deal with is currently scrambling to ditch Ubuntu 10.04 before it loses support in April this year. That's 5 years old now. Companies don't upgrade for fun.