It seems like more than an implementation detail to me. If Twitter receives a DMCA notice and deletes the image, it will immediately be deleted from all of the sites embedding it. When the publishing, distribution, and unpublishing are entirely under someone else's control, it's really hard to justify treating a link as infringement.
BTW I know you're talking about the way judges actually tend to interpret these things. I'm talking about the way they would interpret things if they had any sense.
With your ebook example, if the ebook "auto-loaded and displayed that content for the user" then you're describing something completely different from what happens when a site links to a tweet. It's more like if the ebook reader parses "Encyclopedia Britannica volume B, page 38" whenever it appears in any ebook and embeds the contents itself. If Encyclopedia Britannica is violating someone's copyright on that page, it's just crazy to hold the ebook publisher liable.
BTW I know you're talking about the way judges actually tend to interpret these things. I'm talking about the way they would interpret things if they had any sense.
With your ebook example, if the ebook "auto-loaded and displayed that content for the user" then you're describing something completely different from what happens when a site links to a tweet. It's more like if the ebook reader parses "Encyclopedia Britannica volume B, page 38" whenever it appears in any ebook and embeds the contents itself. If Encyclopedia Britannica is violating someone's copyright on that page, it's just crazy to hold the ebook publisher liable.