At least they're consistent. This is how they've operated since Doom. iD is very generous with how they've interacted with the community -- I can entirely understand their trying to control the element of surprise.

On the one hand, they probably don't want to encourage reviews based on concept art and test renders. It could give people misconceived ideas about the final product.
On the other hand, it could be a turkey, and the leaked stuff might give that away...

Um hello, they leaked it themselves, on purpose.

Er, they're generous with the community except when they blacklist you for life?