Enterprise was involved in a complicated timeline war from way in the future.
When Nero took the Narada into the past he changed the timeline (e.g., he blew up Vulcan!). This means the future of that timeline was changed, which means the past timeline of Enterprise changed too (because its past was causally enmeshed with a post-TNG future).
Nero changed the future.
Enterprise was causally connected with the future. A huge chunk of the Enterprise narrative depends heavily on the time war (including character arcs, relationships, and the purpose mission of the ship). Enterprise characters were communicating, cooperating, and conflicting with factions from the future.
Nero, by necessity, changed any and all aspects of the Enterprise story that depended on future events that Nero changed.
And where is the "temporal police" in all this?
Word of God (Bob Orci over at Trekmovie.com) says it's a branching timeline beginning in 2233, that it's one shared history up until that point. And since it's a shared past, it would include all the time travels up and down from the prime-branch (and other branches) of the future and thus include the TCW, First Contact, Time's Arrow etc.
This is the Holy Bible of Star Trek time travel. It takes dozens of seemingly incompatible time travel Treks over 45 years and makes it seem as if they all function as part of a single system with a consistent set of rules. It explains a lot of the TCW, exposes Future Guy, gives us a look at the DTI and a peek at the uptime agencies seen in Voyager and Enterprise and how they all interact. Plus it's an excellent story in it's own right. Highly recommended.