you could make the case that they are actually scamming potential users by showing them posts that aren't labeled by the front end as "promoted content" and lying to them about the earning potential here.

Some, albeit not much, of the content in Trending hasn't been promoted. It would be cool to stick a label on every post that had received a bought vote, again though, I doubt this is on steemit.com's priority list, but could be easily implemented and appear on other front-ends.

I don't think there is anything to discuss from a legal perspective, but agree it is false advertising :)