I initially approached the question from a live-theatre perspective, because that's my background. Now, after looking into it a bit more, I'm not sure if the modern cinema/playhouse distinction between -er and -re is as clear as some American observers believe. The reality of usage appears at first eyes to be fairly arbitrary, at least when it comes to the movies.
For example, Carmike Cinema owns both MNM Theatres and Muvico Theaters. When Regal bought Hollywood Theaters, they re-branded a load of them as Edwards Theatres. It doesn't appear to be a particularly firm regional distinction either: Cinema West Theaters and CineLux Theatres are both based in northern California. Two of the three largest movie chains in the States, Cinemark and AMC, use -re in their official corporate names. The other one, Regal, doesn't use the word at all in their name, but of the two brands most associated with the group, one uses -re and the other uses -er.
The prevalence of -re surprised me based on what I thought I knew, but of course my knowledge of English linguistic history doesn't cross the pond very often. I wonder if anyone's taken a serious scholarly look at the word's usage in the States, because it seems like a regional/historical study could potentially be really interesting...
Unfortunately I only do that kind of crap with Latin and Greek, so I'm out. Anyone else want to volunteer?