Leos Klien said
So if you're going to be wearing the T-51b then it was provided to him during the war in anchorage, but since the year is 2077 and it was brought out in 2076 means that they aren't a lot of them around.
So it seems more logical for him to wear the T-45d because it's a great deal more common, however not as advanced.
And in turn I think that's why it was used in Fallout 3, they actually corrected themselves because there's a decent bit of the d model kicking around, but not many b models, this means replacing and repairing parts are very hard to do.
I'm sorry, Leos, I simply don't agree. The T-51b armor was standard issue nearly a year before the Great War. That means that every power armored American soldier was wearing T-51b by the time they were shipped back to the U.S., as well as during the final months of fighting in China. Sure, there would be some T-45ds around, but by the end of the war the military would have been creating as many T-51bs as it could handle, and T-45ds wouldn't be worth their weight in scrap. Maybe it wouldn't be ubiquitous, but there wouldn't be two sets of T-51b armor in all of Washington D.C., especially not when the Core Region was chock full of the things.
And again, read up on the Enclave's advanced power armor. It's supposed to be better than T-51b, it was designed specifically to be better, but in-game, it's significantly worse, especially if those suits are supposed to be advanced power armor mk II...