Monospaced typefaces such as Courier are not commonly used to view
documents outside of DOS, character based terminals and shell windows. In
graphical environments and printing, the width of a "space" or
uninterpreted "tab" will vary widely depending on typeface (Times,
Helvetica, etc.), type size, "style" (bold, italics, etc.), so documents
created today that make assumptions about whitespace by using "space"
characters are going to look real bad tomorrow. Just look at the
progression of documents on the Mac, Windows and Unix as people figured
that out, not to mention proper use of double quotes, capitalization, and
other grammar and punctuation (See Robin Wiliams "The Mac is not a
typewriter" or "The PC is not a typewriter" at your local bookstore).
Scalable font technology (ATM and Truetype), fractional spacing support in
applications, kerning between characters and words, etc. can all change the
look of a document, particularly one relying on the use of spaces for
whitespace. Also, keep in mind that display resolutions and actual dots per
inch (dpi) of monitors varies and higher dpi monitors are becoming more
common (120 dpi has been available for a while).
There is no reason to assume 80 characters per line either.
SuperComputer Systems Division