First off Twister is its own network. They use libtorrent and therefore most of BitTorrent's tech (with some alterations). PeerTweet on the other hand actually uses BitTorrent's mainline DHT network. Then they also include ability to assign names to your feeds based on blockchain mining - again this is their own blockchain. PeerTweet doesn't do that and instead perhaps relies on others to build that functionality on top of it (hint namecoin).

I'm not saying that having your own network for everything is bad, I'm just stating the differences :)

Also I think we need different tools that try to do the same thing (ex. Twitter) using different methods.