With all the available options why would you want to use a service that requires you to figure out if the other person uses an iPhone?
iPhones are extremely secure thanks to TouchID and Apple's software.
Apple already has payment info for me and a good relationship with banks.
They're normally pretty great at UI and can integrate it into the OS in ways no 3rd party ever could.
It will be built into the phone and come preinstalled so I don't have to convince people to install it.
Apple shows a lot more respect for my privacy than other companies that I could see doing this (such as Facebook/Google) and isn't a company I already despise (PayPal, YMMV when it comes to despising Apple).
Let's look at this a different way: no one has cracked this potential market yet (at least in the US, just nibbling at the edges)... what makes you think Apple can't make a good play?