Is your thinking that given the choice of powering down and voting, the whales would choose to power down instead of vote, and hence whale voting would be eliminated entirely from the eco-system?
Do whales actually make a lot of money from curation? If they don't (and I think the rewards have dropped from the early days), then they'll simply continue to power down, so the selling pressure on steem will remain.
Depends how they vote right. Smooth made 3000 sp last week, dantheman made 700 and donkeypong made 100 (all estimates). Just some random whales I chose but just check their curation rewards if you're curious.
If you are asking a whale to choose between powering down for $20,000 a week, and staying powered up to earn $3000 a week, they'll choose the former.
So there won't be a let up on the selling pressure on steem (and the whole idea behind the proposal was that it would stop them selling - but it won't).
Some are voting to make money while others are not. If you have a lot of SP, then you make money voting anyway. But much of my voting has been upclicking Project Curie's chosen posts and following AFTER whale votes to add a few more dollars for those deserving posters. One can use votes to make money or to help allocate it to others.