Original Stratego FTW. The Marshall is 1, the General is 2, Colonels are 3.
I don't know why they changed it, but my guess would be that people were too stupid to realize that a lower number can be a higher rank, so they switched them around. The pieces have changed over the years, and I'm okay with that, but I still get screwed up when I play with a newer set with the numbers all "backwards".