IC Markets commission structure

Hi guys,
Please, help me to understand IC Markets commission structure - the round-turn commission is $7 AUD per lot for AUD accounts, but for USD accounts the commission is $7 USD per lot.
So, for example, buying 1 lot of EUR/USD will cost $7 AUD for AUD accounts and $7 USD for USD accounts.
But $7 AUD is obviously less than $7 USD!

Does it mean that the commission is smaller for AUD account and so the trading conditions are better for AUD accounts? I honestly checked the spreads and prices of 2 trading accounts (AUD and USD) and the spreads are the same, only the commission is different ($7 AUD vs $7 USD).
Does anyone know how it works?
Cheers!