If you add the days, then the months, and then the years (rather than the other way around) it does work:
? DateAdd("d", 27, #2/2/10#)
3/1/10
? DateAdd("m", 10, #3/1/10#)
1/1/11
? DateAdd("y", 2, #1/1/11#)
1/1/13
It's not the most reliable method for determining the difference, given that...