> a piece of punctuation that is not widely used any more in modern writing and style guides

I don't agree with this particular point. Wikipedia's Manual of Style [includes a section on the correct usage of the semicolon](http://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style#Semicolons), the APA style guide includes a section on [when you should use a semicolon](http://www.apastyle.org/learn/faqs/use-semicolon.aspx), the Guardian's style guide [has an entry](http://www.guardian.co.uk/styleguide/s#semicolon) on the semicolon...