If you go further, you could say that the glyphs of the letters themselves are skeuomorphs, in the same way that icons are.
When it comes down to it, buttons are a simple and effective interface, regardless of whether or not they represent some physical or historical analog.
If you're going to say buttons and tabs are skeuomorphic, what isn't skeuomorphic? Interacting with a CLI resembles the back-and-forth query and response of conversational dialogue: it's skeuomorphic too!
Here's a question for you: what, exactly, is wrong with using metaphors for existing, well-known analogues to convey information in a new context? Isn't this how languages, notational conventions, and symbolic connotations naturally evolve among humans? I understand why people are tired of Apple's excess, but what's the problem with skeuomorphism per se?