hmm, i hadn't thought about that, but i suppose a 180 minute movies gets half the showing time as a 90 min movie, so might generate half the revenue if it were in the same number of theatres.
one thing that helps it out though. (not sure where i heard this, but i'm pretty sure it's true.
i thought that movie theatres send over 90% of the revenue a movie generates the first two weeks to the group that made the movie. after two weeks, that percentage drops lower and lower. so theatres have an incentive to keep movies with some longevity around. in the long run, this could help out LOTR more than some others, since
1. it's worth seeing again
2. i still think people are scared to try and see it the first week or due to overcrowding fears.
just my opinion.
oh yeah, and lets not forget that this movie will also likely be a big hit with adults, who have read the book. they usually aren't the big "opening day" crowd.