As for “Star Wars”, Peary addresses that in his 1980 book by pointing out that “Star Wars”, while it does have a devoted following, it’s also still sold to the mass audience. Back then, it was rereleased to theaters several times, widely, competing with new movies. I would agree though that it’s an iffy point. Especially over the years.
In the introduction to the cult movie section on my website, I wrestle a little with the definition myself: http://www.theconstantbleeder.com/bmoviescult/introduction/