Now that the poll is over, I can say this.
The flaw in this poll that proved to me it doesn't have IP detection is that you could open the site on a different web browser on the same computer and it would let you vote. Or at least, I presume it would. I never actually tried to cast a vote on the other browsers after voting on one. I voted on Google Chrome, which showed the "you can only vote once" message any time I tried opening with Chrome. But when I opened the page on Microsoft Edge and Mozilla Firefox, it allowed me to see the options and all as if I hadn't voted.
I suspect - but never tested - that Marvel's poll was using browser cookies. If that's the case, it might have been possible to clear the cookies and put in vote after vote on the same browser, too. I can think of other things people could've done if browser clearing wouldn't have worked, but they get more inventive and less likely.