The dev team for Steem mostly builds the Steem blockchain. They also run Steemit but the blockchain is their focus. Every action you take here - posting, commenting, voting, managing SP - is a blockchain action. Steemit the website is just a way to display them.
There are other people who have built other ways to display the same blockchain, and SteemPeak is one of those. (So are busy.io, d.tube, and a bunch of others.) They're basically all skins for the same system.
Ah that makes more sense, thanks for the information, I appreciate it! I'll look into the various other skins you've mentioned and what their added benefits may be. :D