I'd hate to spoil your revisionist history, but Windows has supported IPP out of the box since Windows 2000 (in 1999), right around the same time CUPS had its very first release.
CUPS did not invent IPP.
What eventually became IPP was initially proposed by Novell ('memba them?) back in 1996.
The difference is Windows already had this entire ecosystem of legacy print drivers whereas Linux had barely-functioning print services at the time. It's easier to move to something new when you can scrap the past wholesale.
It's amazing that Linux (and Mac and Solaris etc.) having decent printing is largely because of the work of one guy.