I am not very sure about this but the missing .25 might be something European or just not American. The Euro and the Romanian Leu do not have 0.25 as well. http://en.wikipedia.org/wiki/File:Euro_coins_version_II.png The British pound does have a quarter but it is rarely used.
For some reason, the whole quarter thing makes me think of the American unit system and esp. the fact that 1 quarter of a  gallon is approx. 1 liter here :)