I see this rather in favor for Mac OS X as their upgrade system definitely works, 10.8 is not old at all (2012), Windows NT is from the 90s mostly pre-internet. It's putting things into perspective.
Also there are many valid reasons to not upgrade from NT...
Not if you expose your machine to the internet!
I suspect NT wins unless there are unpatched TCP/IP exploits.
I wonder what percentage of in-use ATMs make a similar bet.
There are some nt machines chugging along doing specific tasks that will outlive us all.