I never thought that votes, etc. would be that important to what defines social media and would have included forums in it. But if I think of social media as "that thing that's addicting", then yeah, the feedback metrics are what make it addicting.
Otherwise, I would think of "social media" as places where visitors get the opportunity to be equal participants. Anyone can post, anyone can comment in places like these (including forums), but in a blog only one can post and the rest comment.
And popularity metrics facilitate mob rule. Lone voices of dissent get steamrolled.
Reddit is especially bad, IMO. It's almost like it was designed as a confirmation bias engine.
The frustrating part is that voting systems also solve a genuine quality-filtering problem. HN does a good job of balancing the costs and benefits, but I suspect there are other viable approaches.
Otherwise, I would think of "social media" as places where visitors get the opportunity to be equal participants. Anyone can post, anyone can comment in places like these (including forums), but in a blog only one can post and the rest comment.