He did say “For most processing”, not for all processing, and he still may wish to search the strings for ASCII values, etc, without worrying about whether or not bytes with the high bit set represent part of a UTF-8 sequence, a S-JIS or EUC sequence, an ISO character or some Windows CP character.
That was my problem with Julia from the start with the lack of any “BinaryString” type, and the issue that if you used Vector{UInt8}, you couldn’t even use the string operations for concatenation (‘*’).