Hello, I created this site. The qualifier of 'usually' means that there's not actually a fallacy being committed, rather a very generic statement about how fallacious reasoning is usually at play when people are wrong (which is certainly true).

You're right that the logical coherence of an argument doesn't have any intrinsic bearing upon the proposition that it supports being either true or false, but this does not invalidate the point that when people are wrong, they're more often than not guilty of committing fallacies in both their reasoning and their defence of their point.

Also, the idea of the site is to be very simple rather than comprehensive. Preaching to the choir is all good and well, but I'm more interested in spreading knowledge to children and people who haven't been exposed to or understood these concepts previously (however many uber nerds have emailed me saying that they've enjoyed it and hung the poster up).

From the FAQ section: The point of the site is to make common logical fallacies easily understood, so listing every single one isn't really what it's about. If you want to learn more about logical fallacies check out this comprehensive interactive list of all the formal and informal fallacies.