The user-facing file is called "Acornfile", with no extension at all. We do not use .cue for anything a user would see. You're looking at files that are an internal implementation detail (and are valid CUE).
Having looked at the product more, I can see how people are getting confused. You expose CUE without saying it. As more people continue to adopt CUE, they will see the CUE in acornfiles. It's obvious to anyone familiar with the syntax.
There are several other issues with Acorn that seem to go the opposite way the market is going. I'll not relay them here because the other places we've conversed make it seem like you don't want any feedback critical of your product.
Again if there's an Acornfile still called .cue somewhere, it's an oversight. You've pointed out an actual example now, so it's been removed.