American Express is largely a transaction company; they make a tidy income on their lending activities, but their largest source of revenue is the "discount revenue", the fees they charge merchants for accepting each transaction. Their card fees combined with other commissions are also, in aggregate, larger than their net lending income.

http://about.americanexpress.com/ar/2010/financial_results.a...

Click on "Consolidated Financial Statements".

So I'm sure they are happy to jump into a system like this that facilitates using their systems for the transaction, but they will mightily resist anything that tries to replace them directly.