Well, sure, that's a cynical but also accurate description of the difference. The other, on a plaintiff level, is that they might be happy to turn a blind eye to student activity in the interests of 'helping' society in that way – whereas a for-profit company can and should be paying for anything they're directly profiting from.
Obviously, under law, a student should also have to pay. I'm merely saying that an IP owner might choose to let it slide. So, y'know, that's a difference too. If a more idealistic one. :)
Well, I'm no copyright lawyer and no enthusiast of the topic, but your confidence suggests you might be?
I can't access the article anymore, but where you've said "if they're suing over summaries of their books" — aren't they suing over OpenAI using the entire text of their books to teach ChatGPT?
I've just done some quick googling, because your post led me to wonder, and it seems Cliffnotes is considered fair use because it summarises the books, using snippets of text for that purpose only.
Whereas, if OpenAI is using their books to teach their AI, they're effectively creating derivative works every time those learnings are used in a chat response — especially if the request is "write this in the style of Sarah Silverman".
Again I'm no lawyer, and maybe their case really isn't strong enough, but the above distinction seems like a reasonable starting point to me.