I think one of the things that some people miss in the Akira vs NX debate is not so much that they used a 24th century design...to me the issue was that they used a clearly Federation design.
One of the big issues that I had with Enterprise was that it did not take the time to establish Earth as a unique entity culturally from what would become the Federation. As it stands, on a purely asthetic level alone, none of the alien members of the UFP brough anything to the table when they established the Federation. The implication was that everyone simply agreed to adopt Earth technology and designs for their new alliance. To me that sort of undermined the philosophical foundation of the Federation.
Given that the Phoenix was shown with modified warp nacells, froma design perspective that should have been Earth's contribution to federation starship design. I would then expect that perhaps the separate engineering section from the Vulcans, the Saucer from the Tellarites and perhaps that high level bridge from the Andorians. In essence we should have seen parts of the Enterprise in all of the ships on the show, not just the Earth ships.
It's always been my guess that the Federation was a human concept from the get go. Earth entered space with all the familiar alien races already knowing of each others existence. The Vulcans and the Andorians have been feuding for centuries, Klingons and the Romulans apparently have had conflicts before we ever set foot in space. My point is, Earth entered the arena late, but wanting to bring all races together (since us humans are so evolved, tolerant, and naturally a peaceful race

) and so a lot of what we see of the Federation is totally human. We've rarely see an "alien" Captain, or Admiral (Spock the only that comes to mind, but we've never really seen him command a crew as such, and Oh, by the way: he's half human) ... Earth is considered sector 001, Federation Headquarters are on Earth. Very allegorically "American" as the super power of the planet, and in Trek terms, the super power of the known galaxy. We've been a unified country for a very short time, but consider ourselves the police of the world, same as reflected in Trek, Earth is the peacekeeper, Earth is the center of the galaxy... and often they throw the aliens a bone by making the Federation president something other than human. So I think the NX is a Federation design because it's Starfleet that is the greater human component of the Federation, the ships would reflect that design ethic.
The NX looks like a Star Trek ship... it's a Star Trek show, it makes sense to me. As far as the Akira debate, many posters here have proven that the NX, while does have hints of a retro graded Akira, it's far beyond just that ship turned upsidedown. If you look at the Akira from different views (side, rear, underside) you can see just how different it really is from the NX. You can find all these views of the Akira and the NX on the Drex Files blog, including Doug Drexler's comments on the debate... but regardless, the NX is nowhere near a "rip off" of the Akira design. It's a Star Trek design.