The usage of dice in a board is just a clever way to simulate percentages. Every increment on the D20 is 5%. So if a card designer wants an ability to have only a 25% chance of occurring, the power must be written to require a roll of 16 or higher to be successful. The use of higher or lower numbered dice only affects the accuracy in portraying a desired percentage. However, since the percentages portrayed won't be in clean 5% intervals, it will not be necessarily better to use any dice other than a D20 for such purposes.