Is “steemit” the only platform on steem blockchain that allows you to earn from upvote?

Yes, it is only steemit although other platforms linked to steemit do upvote you if you post on their own sites. Now, Steemit is such in that way that is why it is unique and other blockchains can and might eventually crash but for steemit, it is just like the new and articles site so it goes on and on till it becomes more known and it's currencies rise as much as maybe the Bitcoin.