> This is how it was always done, back in the infancy of usenet*. To assist the reader's recollections of what was said, there would be a quoted part signified by a > (or |) and the new poster would reply underneath the quoted part.

This was also, for reference, the accepted standard on the old BBSs (at least in my area). The standard BBS formats (Renegade was the big one around here, but we had some others) *all* defaulted to quoting like that, though many of them also used different text colours for quotes.

I agree with Wolf and Sam in saying it's that way because that's the *best* way. And I now feel quite old. Thanks, guys. :-}