I see your point... but.

The reason this wont turn into anything as bad as a bid bot is because... we have free downvotes and curation rewards oscillate so much that 4% means little to nothing.
If you want to maximize picking a good curation target far outweighs the gain from those 4%.

I see this more of a token of appreciation then anything else.
The benefit is on the author side actually imo. Not having to powerdown has value and id say that value is greater then the 4% loss.