Earlier quoted context omitted.
hahahahahahahaaa you have no idea the vast amount of windows code that is emulation layers to ensure that other companies legacy users can continue to use programs designed for dos, windows 98 etc. Google doesnt have to do it, but like i said thats why the c levels insist on microsoft even when their products arent anywhere near the most elegant, feature rich, or performant.
That's supporting their own legacy products, not other companies'.
I can't speak to the emulation layers, but there are tons of verified stories about MS writing special code that actually watched the running processes and adjusted the behavior of the OS. They'd look for popular apps that utilized bugs/quirks in older version (which were remedied in new updates) and essentially emulated that bug for that one process to keep it working in the new version of Windows. Crazy, crazy stuff. Sim City was a famous example.
From Joel Spolsky: "I first heard about this from one of the developers of the hit game SimCity, who told me that there was a critical bug in his application: it used memory right after freeing it, a major no-no that happened to work OK on DOS but would not work under Windows where memory that is freed is likely to be snatched up by another running application right away. The testers on the Windows team were going through various popular applications, testing them to make sure they worked OK, but SimCity kept crashing. They reported this to the Windows developers, who disassembled SimCity, stepped through it in a debugger, found the bug, and added special code that checked if SimCity was running, and if it did, ran the memory allocator in a special mode in which you could still use memory after freeing it."
I'm no fan of MS, but that example speaks to a respectable dedication to a principle – rightly or wrongly.