I'm on mobile and can't find the link at the moment, but somebody at Microsoft (Raymond Chen maybe?) did a blog post about Pinball and why it's not in Windows anymore and not likely to make a comeback. IIRC it was written by an outside company, and the code is extremely hairy and was deemed too much effort to port to 64-bit for the return they'd get.
The last line is: " Hey everybody asking that the source code be released: The source code was licensed from another company. If you want the source code, you have to go ask them."
Which seems like a cop out. Microsoft you've got clout, make the deal.
Just hurry up and release minesweeper already, and stop teasing us!