There are old games that don't need emulation to run fine on modern OSes. Age of Wonders (1999) would be one example.
For old software that's not games, it's actually more common than not, because the OS really didn't break the userland contract all that much - what it broke is various undocumented assumptions that software was relying on. Games tended to be the kind of software that did it the most, usually in the name of performance (and sometimes also DRM).
Although if you unwind to before Windows XP, you also have to consider the Win9x/NT divide. Most games of that era were written for Win9x, and often relied on the liberties offered by the very lax process and memory management model. The transition from 9x to NT - which for most consumers happened via XP - was definitely a big userland breaking change for anything that didn't care about NT compatibility before.
(That's why the sweet spot for back-compat is circa 2005 - XP was already well-established, so all new software was written with it in mind - but technologies used were still of the older variety that doesn't drastically change every two years.)
For old software that's not games, it's actually more common than not, because the OS really didn't break the userland contract all that much - what it broke is various undocumented assumptions that software was relying on. Games tended to be the kind of software that did it the most, usually in the name of performance (and sometimes also DRM).
Although if you unwind to before Windows XP, you also have to consider the Win9x/NT divide. Most games of that era were written for Win9x, and often relied on the liberties offered by the very lax process and memory management model. The transition from 9x to NT - which for most consumers happened via XP - was definitely a big userland breaking change for anything that didn't care about NT compatibility before.
(That's why the sweet spot for back-compat is circa 2005 - XP was already well-established, so all new software was written with it in mind - but technologies used were still of the older variety that doesn't drastically change every two years.)