What is the typical Android OS Upgrade policy?
There isn't a specific Android OS Upgrade Policy. If it's a Nexus device and it can handle the latest version of Android it will get the latest version of Android from Google. Other than that it is up to manufacturers to update drivers and their specific customized version of Android for their own devices and then it is up to the carriers to approve those updates and release them to users' phones. 

Apple has only one phone basically and they release updates on what seems to be a yearly basis and update is done via their own service, not restricted by carriers.