[tenebrisalietum]

I'd have to look into it, but I think the whole reason for text vs. binary demarcation is the fact that ASCII text (not Unicode, old-school ASCII with valid characters 0x01-0x7F) could be sent over a 7-bit serial interface and binary needed that extra bit so you had to introduce overhead to make sure everything reached the other side. Because you might have had actual 7-bit serial (or less) teletypewriters connected in the 60's.

[dhosek]

On DOS it also came into play in how line endings were handled.