For some reason Samsung decided a decimal point isn't necessary for the numeric keypad on their phones. There's not much we can do from this end about it. If you're experiencing this problem you can visit this page on your phone:
http://m.fuelly.com/disable-numeric-keypad.gas?id=1
That will tell Fuelly Mobile not to use the numeric keypad for entry. You'll have to navigate to the numbers each time, but it's better than a non-functioning numeric keypad.