Brannon Braga himself at the time said that Enterprise happens in an alternate timeline, created by the events in First Contact. And that works fine for me. I'd even go so far that nuTrek is the continuation of the NX-01 timeline, which would explain a lot of the differences that were there even before Nero screwed up the timeline. The question is, which timeline were Nero and Spock Prime from? Did Romulus really blew up in "our" timeline or did it happen in the alternate Enterprise timeline?