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comment voting for users that are not actively posting was always part of the plan, but it was not supported by the 3rd-party services we were using.

We released our own fully automated solution a month ago, and we added comment voting two weeks later after everything else was running smoothly and VP had stabilized.

We do not believe that top-level posts are the only valid contribution to Steem (in fact we think comments are very important!) so while our system still exerts a preference toward top-level posts, it will resort to upvoting comments if somebody is not receiving their subscribed value through posting.