Bitmessage is for any messaging system. You can broadcast (twitter), send private message (email), or start a channel (IRC). The key in bitmessage is that to send a message you have to do a POW according to the size of the message you are sending.

Even then you still have massive data bloat problems, which I dont see DHT alone solving.

Reading Bitmessage broadcasts requires following the user, so you can't see replies if you're not subscribed to the replying user. Twister feels more like Twitter, including searching, hashtags, etc.

Though I guess you could leverage BM's protocol and infrastructure to do that too (broadcasts are public you'd just have to filter the noise).

The few times I installed bitmessage to see what it looked like it escaped me I could actually broadcast messages à la twitter. Might check out that part of the package in the coming future. Thanks for pointing it out.