Thanks for the comment!
You're right about that. Any of the front-ends could add a beneficiary setting in posts by the referred account that directs rewards to the referring account. It would have to be a big enough percentage to encourage referrals, but small enough not to drive people away to post through other front-ends, though. And I guess they'd have to maintain a database of referrals (or else store the info in custom_json the block chain.)
In Tsu's mechanism, the rewards don't appear to cut into the content-creator's share. If I'm understanding correctly, it comes out of the site's share of advertising revenue. On the other hand, beneficiary rewards here come out of the author's share. Maybe not a "show stopper", but it is a slightly different dynamic.