Six Things You Need to Know About ATMs and the Windows XP-ocalypse
bloomberg.com
bloomberg.com
So while MS could have, theoretically, decided to keep releasing fixes for XP Embedded as well as for XP Home/Professional, it has decided not to.
Note that the Embedded version is stripped down a lot, thereby reducing the attack surface (and the amount of code that still needs to be supported) significantly.
Alas, I wouldn't go that way now, unless I really, really had no other sane choice but stay with XP. That was the case in 2005, but not today (I understand the case for embedded systems and/or specialized SW; this is generally not the case for most users - and "we absolutely need IE" is, thankfully, no longer a majority issue).