That's because 4-siders are dangerous if stepped or sat upon. Also, they don't really roll, do they? Just sort of thud onto the table. And none of mine seem to know that there's a "3" or a "4" on them. That's why I'm glad that Paizo took all of its hit dice from d4 to d6 in PFRPG. Used to hate playing Wizards but no more!
M