And in 3.0, Python is adding a bytes type, so b"foo"[0]==102
Obviously both ways are useful. If I had to guess what Arc ends up doing, I'd guess : whatever leads to the programmer having to type less tokens, or whatever facilitates clever macro definitions, leading to same.
I would suggest that marking a literal vector of bytes is not the most useful role double quotes could play. Python has a lot of history of using that, due to exactly this kind of confusion of strings and vectors of bytes, leading to b"", u"", etc.
