In regards to Microsoft Word, it might be exactly to scale if your monitor happens to be a multiple of 96 DPI: https://www.anandtech.com/show/11050/the-microsoft-surface-s...
But I'm designing when I'm in Word, it's not necessary or convenient to do all of my work at 1:1 scaling, that's what the ruler is for.
Compounding the problem is that the operating system relies on the monitor reporting its physical size correctly via EDID and for a lot of vendors (most notoriously Dell) this isn't guaranteed either.