The sealed O-rings contain lubricant for the internal surfaces of the rollers within the chain. The outside of the rollers need lubrication as they contact/rub against the sprockets' teeth, as well as the side plates rubbing against the rollers. Ideally, the drive chain would be bathed in oil, just like the valve timing chain, but the chain and sprockets of the final drive system are exposed, no oil bath, just what we occasionally spray on them, for lubrication.
There are chain oiling systems, with 100% loss: they drip motor oil onto the chain, in a measured fashion, giving the chain, and sprockets, a continuous, fresh coating of oil. They're expensive, and they create a mess in the hind-quarters of the bike, but they will double, or triple the life of the chain and sprockets. Here is a link to some additional information on them:
Scottoiler Review;
Cameleon Motorcycle Chain Oiler;
Scottoiler eSystem Review. Those will give you a better idea of the why's and how's of chain oiling. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII