Though, Microsoft keep putting off XP's death might have meant that they thought it would continue being supported again so didn't think about upgrading.
Windows XP's lifespan was extended due to the Vista outcome. However MS jumped the gun too quickly, as Windows 7 more than made amends for all of the OS's shortcomings. Had XP followed MS's normal support timeframe, it should have ended about 1 year after that of Windows 2000 Professional (W2K's support ended in the summer of 2010), which until SP2 for XP was released, was the "go to" OS for business needs.
Hopefully, in similar fashion, Windows 7's lifespan will also benefit for the same reason, it's successor is a bust.
As to the banks, again, they had the time & funding (from the extreme high interest of predatory lending) to upgrade every ATM machine on the land, at least those on US soil anyway, many has been built in more recent years. It's up to merchants which type of POS systems they employ. There are alternatives to XP POS computers in the checkout lanes, though I see that some still uses this. Some where it's obvious, for some transactions, the sales associate will have a computer at the register, with a "Microsoft Dynamics" screen, once logged on, the familiar XP Start Menu is there & can be seen.