Banking systems don't need impenetrable security for people to use them. People pay online and use online banking every day from easily compromisable laptops. They do so because banks and credit card companies have good fraud coverage (unless you're negligent).

I think the real reason for Apples worry is that they want people to trust the smartphones for way more then just payments, for instance Health information. And people might just end up much more reluctant to do so if they know the phones are easily hackable.