If a user that was happily using version 727 is now on a version that's almost identical to 402, they're now missing 300 versions' worth of code changes. You don't see how that's an issue? What if they were using functionality from that? Upgrading to 728 has removed all this code they were depending on!

If everyone follows your advice to upgrade, then everyone has this problem. Including you, unless you ignore your own advice.