The basic problem is simple:

PEOPLE DON'T UPGRADE.

They just won't do it. You can make it as annoying and intrusive as possible. You can make it flash warnings in big red letters. It doesn't matter. People just won't click the damn button. When you ask them why, they'll usually say something to the effect of that they don't know how, or that upgrading once broke something somewhere... They simply refuse to do it, no matter how much you try to explain or warn them.

There is only one solution to this. Google found it with Chrome. Upgrade them automatically, and don't bother telling them.

This is the only solution that will work in the long term. We have to implement automatic upgrades. We have to make it happen entirely without the user being involved. That's the only way it'll get done.