People --
there is a lot of literature on the most readable line-length.
I'm not going to summarise it here -- I'll give references to books
on typography if you want -- except to say that a measure (line-length) of
from ten to fifteen words is acceptable, with 13-15 implying a much slower
reading speed and therefore being limited to heavier, e.g. technical or
specialised, texts.
Newspapers use short columns for other reasons.
The margins are known to play an important part in assisting the reader's
eye in locating the start of the next line.
Lee
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Liam Quin, Manager of Contracting, SoftQuad Inc, +1 416 239 4801
lee(_at_)sq(_dot_)com