Looks like Apple's commission is ~15-25 BPS for participating banks (from those banks):
"The biggest “surprise” over last 2 months is that Apple has squeezed 15-25bps from the 5-6 participating banks at launch (C, BAC, COF, JPM, Amex and perhaps WFC)."
In finance, 1 BPS is 1/100th of a percent. So Apple could be pocketing ~0.2% on all transactions.
The US does about $12B in card transactions per day. This means that for every 1% of US transactions it captures, Apple could add ~$80M to the annual revenue which is a very small amount against its $140B revenue. Yes there are international markets, but still this is not done for profits by itself.
