Yes, it is a statistic you can build an argument on. I don't know what business background you have or where you are founding your beliefs on, but they do not exist in the real world.
DC's livelihood, and that of his staff, are dependent on the contributions of patreons. Therefore, in order to maintain, or increase, that aspect - it is in the best interest of the development team to address those options provided that are most supported by those who contribute to that livelihood. It does DC no good to get input from those who do not subscribe which may, or may not, influence the outcome of those polls. If voters who are not subscribed overrule those who do subscribe and DC follows it, it can cause 'buyers remorse" as well as increase the sense of futility in donating (i.e. "why should I contribute if people who don't can overrule the wants of those do contribute"). And should enough of that feeling pervade the subscribers, DC could see the number of patrons decrease and therefore his livelihood - and those of his staff - become less secure.
Before you say "well, if people who aren't subscribed were able to vote and their desires prevailed, DC could look at a potential of increased income from new subscribers" - while this is a good hypothesis, there isn't much validity. It goes to the old "bird in the hand is worth two in the bush." And again, you're putting your nut over the food on the table of the development team. If you want to influence the content based upon the options made available in polls, subscribe to vote.