Well since the "unwashed masses" wouldn't know the NX-01 from NCC-1701 or the NX-2000, why couldn't it be the original ship?
Because the original ship looks like a product of a '60s TV show and not a 2009 blockbuster film?
On the TrekBBS, somebody took the new Enterprise and showed it around to a few people they knew who were causally aquainted with, but not big fans of, the original Star Trek; the reaction was "oh, that's the ship form Star Trek."
It's a funny thing, people's memories. When ILM was putting together the digital Yoda for Episode II, they tried replicating the non-moving lips of the puppet version, only to find that they didn't play on the CGI version. People, including the poeple working on the project "remembered" a more dynamic Yoda than they actually saw in the form of the puppet. Similarly, if you throw the '60s ship on the big screen, in a modern theater for a modern audience using modern techniques... people like that would look at it and think it looked way cheesier than what they remember seeing form the old TV show, because the context has changed. And for people who may never have seen Star Trek at all, and were raised on modern film aesthetics, the simple '60s design could be fatally laughable.
And you'd better believe that's what this film needs. What's with this reaction I keep seeing of treating talk of Star Trek as a product as though that's some kind of sacrilege? Trek is entertainment. If Star Trek is going to survive, it needs to change and be, yes,
marketed to a new generation of moviegoers. You've got 700 hurs of old guard Trek you can go back and watch, if that's what you want. It isn't going anywhere, but I'm waiitng to see what comes next.