1. The biggest difference is definitely the RxJS observable support, which solves a lot of model problems in an elegant way.
2. I wish I had some examples published (we have a few internally), but having RxJS observables actually do a phenomenal job of dealing with the animation problem (think .delay() state and bi-directional communication). I hope to be able to update the docs soon with more details.
3. Aside from those you mentioned, performance was another big problem. React is slow (not as bad as Angular), but more importantly because the code was so complex I was unsure if we could modify it to meet our needs. At Clay.io we push the boundaries of what Mobile-web can do, and performance is absolutely critical. I realize this answer is still sub-par, and I agree, Zorium was mostly build off of Mithril and just happened to look like React in the end.
Edit: It's also worth mentioning that API design (in z.router) and application structure are what took the most time. Because Zorium is built on virtual-dom there isn't really much custom code.