Please don't underestimate the privacy implications as once you have signed into the app store, you're signed into all the other apps too. I would much prefer to have a regular exe with a serial.
The credit card being in Microsoft's hands is just another surface that my card is exposed to, perhaps I'm being over zealous worrying on that front.
A bit surprised by the remark about credit card number: of many tech companies, Microsoft is among the last I'd expect to mishandle it.