4 hours, or the next flight out if it's more than four hours after you arrive, is the maximum length of time for a stay not to be considered a stopover. If you want to stay for longer than that, if you could continue your trip within that time frame, it's a stopover.

And why shouldn't it be? Since "stopover" means you're staying someplace longer than you have to en route to what you say your destination is, I don't think this is unreasonable. I don't know why the international rule allows longer stays, unless it's to let people adjust to time changes (without the added complexity of making up different sets of rules for east-west and north-south travel).

As for airlines allowing stopovers on awards - I don't see what the big deal is. Since they already apply capacity controls to the individual flights, why not just let it happen? Why should it matter to them if I take the next flight out of Chicago or another one three days later? Then again, I've never had much luck finding logic in airline rules...