To understand Salt, it really does help to understand what ZeroMQ is and why Salt was originally based on it. Having a solid foundation of knowledge when it comes to ZeroMQ will also help in getting a handle on RAET. It will also help to understand HTTP and why Salt doesn't make use of it.
It's important to understand that, when ZeroMQ came out, there was nothing like it. There are alternatives now, such as
nanomsg, but ZeroMQ was the first and it came on the scene just in time for Salt.
Many of the design principles behind Salt are inspired by previously existing projects, some of which were in use by Salt's creator at the time of its conception. However, it was not simply a copy of a bunch of other projects hacked together. If existing projects did what Salt was designed to do, then Salt would not have been created. The corollary here is that a number of design principles were used because what was out there wasn't cutting it.