Publishers/creators can choose to show or hide the number of subscribers and their monthly earnings. This site simply is scraping that freely available information.
I would like this type of economy to flourish, as it seems like a very viable way to get good economic support for open-source. However, if this is a common occurrence, it seems developers will continue to be better off working on closed-source.
If supporting someone with X€ is any kind of "vote", it's a vote that they should get X€ more than they currently get for their work. It may be hard to make an educated decision about that, but it's impossible without knowing a creator's current income level to begin with.