I think you're right on that Steemit's lack of ads makes it more resistant to shitty content-boosting. Plus the fact that SP is expensive, so there's no good cheap way to "boost" posts up the ranks.
On the other hand, there is absolutely nothing stopping major corporations from buying a large slice of SP and using it to self-vote themselves onto trending...
I was going that way with my thoughts to. But the community does frown upon circle uhhh votes. And honestly, there are enough of us to see a problem and propose a hard fork before it became harmful.
Right? I hope...