Rebirth was a relaunch in the aftermath of Ultimatum the same way that Marvel Now is a relaunch in the aftermath of Avengers Vs X-Men. Both have been major events that featured consequences for both realities (in the Ultimate Universe severe ones). No continuity was lost.
I understood pretty much none of that. I don't need to. But I have to urge people who understood that to step back and take a good look at wtf has happened to comic books.