I'm not sure it's sensible from nV's POV. If you don't allow reviews until release day, then you guarantee (if you are nV) that you will get masses and masses of pre-orders from everyone terrified of FOMO.
Even people that aren't sure they want one will pre-order to just to be sure they can get one
If you have reviews coming into the mix, they might actually cause some people to stop and think if it's actually the card they need.
Given that nVidia is like Apple (and not like AMD), not having reviews until the very last minute might even be helpful.
Bottom line is, they will generate untold pre-orders on the strength of Jensen's demo and on their name and on the hype.
Reviewers might spoil the party!