Currently the webpage for buying an Antivirus subscription does not allow for multiple years. This needs to change. Bitdefender, Avast, and other vendors allow for ONE, TWO, or THREE years.
And there is some confusion on what "up to three computers" means. One of your most prolithic forum posters said that it's actually only good for ONE computer. If that's true, the description is very wrong. At least offer the choice of ONE or THREE computers.
Also, "quantity" is a fairly useless option. Who would buy multiple, separate 1-PC / 1-year subscriptions?