I was taught that printers, back in Colonial days, thought that
periods and commas looked "lonely" if outside the quotation marks, so
they began putting them inside for aesthetic reasons.

My information is that in the old days, the thin periods and commas were
more delicate, and lasted longer if they were protected by the larger
quotes and parens.

That sounds reasonable, Jose, until you consider that whatever piece
of type comes last in the sentence, it is "protected" by the space
(is it called an M Quad?) that comes next. Each piece of type in the
line is "protected" by the pieces on each side of it.

I'm not defending my explanation, btw; I don't know whether or not
it's true.

vince norris