The D20s that come with Magic products are spindown dice, not normal D20s. The faces are ordered for ease of lifetracking and are _not_ optimized for random rolls.
Because the dice aren't evenly weighted, they have a strong bias. IIRC, Spindown D20s crit somewhere around 30% of the time.
More specifically, in the spindown each number is adjacent to its predecessor and successor. In a regular d20 the numbers are more spread out, and opposite faces add up to 21.
Because the dice aren't evenly weighted, they have a strong bias. IIRC, Spindown D20s crit somewhere around 30% of the time.