"why would police, or anybody for that matter, want "less" lethal rounds?"
I think that what he's getting at is the reduced power SD loads. Not so much less lethal as much as less recoil. With less "oomph", there's less there for the autoloader to tap into to work the action, but still plenty enough to get the SD job done.
OTOH, if less lethal is what you really want, there's plenty enough of that around, common as fleas on a proverbial dog. Like, for instance, light trap/skeet loads -- those are quite a bit less lethal, and less liable to shoot through walls. Some people actually want that. Not only that, but those loads will work in an autoloader just fine. Personally, I'd rather use buckshot and get the job done right.