Some Steemians upvote their own comments. Among those people there are many new users and there are some old users. I have written 4993 comments and have only upvoted less than a handful of them myself and I have only done so because I've had some unusually important piece of information to convey.
Most Steemians I know refrain from upvoting their own comments, too. Why you may ask if most people, if not all, upvote their own posts? Well, Steemit and other user interfaces of the Steem blockchain order comments according to the how much they're worth based on their upvotes. If you're upvoting your own comment, you're pushing your comment above other comments. It is generally considered good practice to allow other people to decide how much visibility your comment deserves in the comment section of a post. It's also considered polite. Aggressively upvoting your own comments is a bit like shouting other people down in a conversation. So, I would like to ask those of you who do it to refrain upvoting your own comments in the comment sections of my blog posts. Thank you very much.