If the majority of people who saw the film were longtime Star Trek fans, the movie would have been the biggest box office bomb of the year. There simply aren't enough people to keep the film franchise viable with only the longtime fans going to see it. Even Nemesis
with its poor showing relied on a hell of a lot more than just fans seeing it.
Plus, that article is discussing the projected turnout in the first weekend before the weekend was even out. Of course there's going to be a higher turnout of fans in the premiere weekend.