Great discussion, I'm really sorry about the situation in the US, the drop of support from BoA and Chase is a big deal and the timing does seem very curious. This is one of those instances where the platform cannot afford not to have the continued support of two of the largest nationwide banks. So yes, the rules are entirely different. As much as I care about the WP platform worldwide, the US is the most important market whether I like or not. The argument that the banks are solely responsible and that all Microsoft can do is shrug its shoulders, is only partially true IMHO.
It's not the banks purpose to make you to use one phone platform over another in order to make use of their services. Mobile banking is becoming more important / convenient but until it becomes an essential service like electricity or a phone line, you have make choices that best suit you. There are still a lot of people out there that don't trust mobile banking or even web-based banking, period.
Now having said that, I also entirely agree with the viewpoint that Microsoft, in this instance, should step in and do whatever it takes to keep these apps alive on the platform. Why? Because for the reasons frequently levelled at WP:- still playing catch-up, the two reboots of OS and app architecture, the need to win mindshare, the seeming treacle-slow trickle of improvements to the OS feature-set, the painful fight with carriers for presence and shop floor space. All these things, when taken as a whole, add up to a big set of challenges on their own so it's not helped when important institutions like banks turn away for whatever reason, particularly when they were offering their support. This is too big, too important to fail.