[ellism]

For what it's worth, I'm the one of the folks that designed the original tuple class (the reference type, System.Tuple, that shipped before hand).

At the time, we picked one based indexing because we felt it sounded more natural when spoken allowed (mirroring saying something like: This is the first Item in the tuple).

I would expect that the design bled over into ValueTuple, which looks very similar to the reference version, except, of course, it is a value type.