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.
Hmm. Problem is, that means stdin is your arc script. For many scripting tasks, you want stdin to be the input to your script, e.g. a pipe or console or redirected file.