> The court seems to be completely disregarding that it was misdelivered into spam.

Spam categorization isn't a delivery issue. The delivery is the same whether you, upon taking delivery, toss the message into a bin labeled "spam" or one labeled "inbox".

I guess it's an instance of a more general principle: sending an email doesn't guarantee it gets to the user's inbox, never mind that it gets read.

Even if you are OK with the idea that a user can be presented updated TOS with no option to disagree (I don't, but put that aside for a moment), it should still require a mechanism that actually guarantees (or at least verifies) that the user has seen that the terms are updated. Email is not that. (An unskippable notice on login to a web service would be.)