It's the fault of the currency exchange rate. You can see such stuff in other games too, sometimes you must pay 11.00€ for 1000G, sometimes you must only pay 10.50€ for 1000G.

Top Eleven does it the other way around, it sets the price per token. One token could cost 0.11€ the one day, and on the other day it could cost 0.15€, which means you get less tokens for 10.00€. It's just an example.