Audiobooks are direct audio transcripts of books. Picturebooks are only called books because of their binding; you wouldn't call the same content in slideshow format a book. Choose-your-own adventure books are books because they are written in the same way that other books are, only with optional page order changes.

The word "book" is misleading anyway, because a book is a format, not a medium. In your above examples, the audiobook is the outsider where format is concerned, as it is not contained within a physical book. On the other hand, it uses the same medium as the choose-your-own adventure(both are created with the written word, even if they are presented differently), while the picture book uses a different medium entirely. In that case, it is probably better to use the word "novel." Still a format, but one that would more closely encompass what the OP is trying to say.

But I still disagree.

Try reading a transcription of the text from a VN without any other context. Does it look like a complete work? No? It isn't a novel then, at least in the traditional sense of the word. Such a transcription would far more resemble the script from a movie or play than anything else. So since the words themselves do not tell the whole story, we have to acknowledge that a visual novel has other critical elements that make up the experience. Unlike novels.

So let's consider then that at least the visual element is required to get the intended experience. This makes sense, given the name "visual novel" after all. The sound is more of an enhancer, as indicated by the fact that you can turn the sound off in visual novels. Music helps set the mood of the scene, and voices(when present) help form a connection to the characters. So far, it sounds like we're keeping to the movie parallel(you can have a silent film, but you can't have a pictureless one). But of course, that isn't entirely correct either, as most visual novels have only very sparse animations, if indeed they have any at all.

I've seen people call visual novels a unique medium, and while I can understand the sentiment, I don't agree with the designation(though to be fair, it's usually in response to people calling it a genre, which is just as wrong). A medium is basic in nature. The written word. Clay. Paint. Sound. Visual novels are more complex than that. At the least, you need three media to create a visual novel: the written word, whatever method you use to create the art, and computer programming. That makes it a multimedia entertainment. Not its own medium, but a combination of existing ones.

Still not very helpful when it comes to categorization though. My preference is to call a visual novel a unique format, but even that is only my way of simplifying things so that I don't have to call them "interactive multimedia fiction," which doesn't really roll off the tongue easily.

So... games... well, the problem is that some really could be called games with limited interactivity, and some have so little interactivity that that it might be more accurate to call them oddly formatted manga with a built-in reader and bookmarking system. I've already given my reasoning on why they might be considered games regardless, but that's only a matter of perspective.

Ultimately, I think that the important thing isn't what visual novels are, but rather how they are presented to people who haven't experienced one yet. Much like how I would introduce a new band to a friend by letting them hear songs that cater to their existing tastes, I would change the way I described visual novels depending on whether I was talking to a gamer, a literature fan, or an anime geek. Within the community here, such considerations are unnecessary. Visual novels are visual novels. What more needs be said?