IANAL, but I think Richard’s point is the question of what the user has purchased if the EULA does not apply. The general view of 3D content is that, absent the EULA, the content is for personal use. It is the EULA that grants the user the right to sell renders made with the content; otherwise you would be selling a derivative work. As an analogy, if I purchase a copy of a movie, I do not have the right to sell prints of frames from that movie, or photoshopped prints of frames; I only have the right to view it. So is 3D Content considered an artwork, which the end user has the right to use privately but not commercially, or is it a tool akin to a paintbrush, which can be used to create items for sale? While software could be considered akin to a paintbrush or movie camera, as a tool, content seems to me to be more akin to a work of art. You can create your own content using software, just as you could create your own movie with a camera, and sell it if you wished, but creating a render using content made by others would be more like dubbing your own dialog into a movie you had purchased. You can use it for your personal enjoyment, and you could sell the original, but you could not sell derivative works created using it.
The movie thing partially a false analogy though, as selling prints of that frame is a direct copy, and thus clearly derivative work. The Photoshop item, on the other hand, might not qualify, depending on how much of the work is that image, and how much of it is original. Remember that derivative works are not an all or nothing item under the law, but rather taken as a case by case basis (Supreme Court, in Campbell v. Acuff-Rose Music). If it can be shown that the change is ‘significant’, then EULA or not, transformativness applies and it qualifies as a new work under the law.
It might seem peculiar (and it is) but under the law, using the example above, if taken as-is, it’s art (maybe, some of them, such as Optitex tshirts, are so broadly generic that they would be questionable). If it’s changed though from the original in some meaningful way, it becomes the paintbrush.
What exactly qualifies as ‘meaningful’ is a good question.
Edit:I’ll add one more complication this causes: Sales records from the online store are no longer sure fire records that someone has or has not bought a product legally, since the private sale of a license, while perfectly legal now, does not provide a big trail of proof to follow, with the burden of proof being on the prosecutor or plaintiff.