I don't think it matters. It's their store, and they can do it. I suspect that if Inkwell was trademarked (which it sounds like it's not), they could bully through the reviewers. Apple certainly didn't have any legal standing to deny my app name, and I likely could have bullied them into approving it, but it wasn't worth the agita.

I do have a registered trademark (not for an app name, though). It's a really painful process. I can see why folks wouldn't want to go through that for every app name. I don't bother, with most of mine, but I do search for other registered marks.