Hm. Other than chance and observer bias, one hypothesis would be that if there are only TWO common states, then they more often have comparative names like "standard" and "premier" and only when there's three do they start to be numbered.

Yes, I've a long rant about how "first and third" got its name, but it's not very interesting. (I am moderately impressed that this, and other tidbits of history, and reported accurately on college websites, although I'm surprised that they HAVE been accurate.)