I think it would only do that if the exchange accounts voted, the rewards distribution is based on actual votes recorded on posts, not possible voting power.
Yeah, that's what I was thinking...
I'm not sure who that dunamo exchange is, but with 190 million STEEM, they could maybe collect some nice fees with a staking service. Might be worth the effort. No idea, but that's a lot of STEEM.
RE: SP distribution by account sizes