I've got a few images with iStock (very few) and $95 on account, but I didn't get the email. I wonder how many iStock contributors have not been notified of this change.
Maybe your spam filter knows better and decided you are better off with out the email.
I can't speak for Pickerell, but I don't have a spam filter. I've received other emails from istock since that one, but I didn't get the tax email.