Emailing you probably seems a lot less anonymous now than it did when they were filling out the survey. Not to get into value judgments over pornography, but with a website, you are telling a machine that you like pornography. With email, you are telling a person that you are a perv.
Yes, but there are a ton of free email services where they could make a new account. If anything, the survey is less anonymous because the forum admins can see how you voted. Given that, do you still think I'd have more success if I automated the process and made it a web service?
According to my theory, the answer is yes. I don't know how much time or money I'd be willing to bet on the correctness of my theory, but I do know that perception is powerful stuff, even when logic says that perception is wrong.