The poll on an open site like ZAM can be voted on by anyone, even if they don't have a FFXIV account and wouldn't be affected by it at all either way. People who have no personal stake in the outcome can still cast a vote, and so the results can be diluted - on both sides- by people who haven't bought the game and/or aren't playing it in the first place.
If these forums were open/public, I'd have the same opinion here.
However, they're not.
Since an actual account and an active character in-game are required to post here, those voting have already invested money and/or time into the game. 100% of those answering the poll here are directly affected by subscriptions being enabled.
Thus, I think the poll results here are far more accurate and telling than that of a poll on ZAM, or some other public site where anyone can vote.