sometimes it seems like Judo refs stop it prematurely..
I was told it is assumed that you are beating them, and that by that time they will be incapacitated.

Ippon throw == knocked out, right there on the concrete.
Wazari == Hurt'em bad, now you're grappling and beating them, until your 20 seconds is up. It is assumed that they are now unable to fight.

But that is just what I've been told.