I don't believe anyone has mentioned the semi-colon's use as "the comma's big brother" in a complex series.

Thus, in a series (of course normally set off with commas) where one of the series-members contains a comma, the "big brother" is called in to control the series, while the "internal" comma remains in place and doesn't cause confusion.

"I gave her expensive cut flowers; imported liquor; and, only on occasion, candy."

If the semi-colons were shifted back to commas, the result would be VERY muddy:
"I gave her flowers, liquor, and, only on occasion, candy." Dave Oesterreich