Daniel,
I know it seems counterintuitive, but your rotary simply doesn't clean like an OP. It's not a question of which cleans "better" - the two pieces of equipment are completely different animals. This is not a knock on rotaries. I have always and always will own rotaries, but that doesn't make a rotary an OP machine.
This is why for most us, the longer we're in this business the more "stuff" we own. There is always the "perfect" piece of equipment for a specific application. Is this a blessing or a curse? Depends on what mood I'm in when pondering all the crap I've accumulated. :?