well moderation is ubiquitous , but yeah -- personalization/targeting/social graph are essentially the things that people expect out of a social media platform.

I do personally think the karma thing is an aspect , because it's gamed everywhere to huge advantage -- but the altruistic view is that its a branch of moderation, an effort to democratize the removal of obviously bad actors while still facilitating dissenting or contrary speech.

I also know that's a naive view.