OK, I finally seem to have found a concrete mandate on this issue after digging a little deeper. Not sure if I should reference my source as a valid one since it's definitely not official but I'll let the readers be the judge. Here's the link: Quotation Marks: Where Do the Commas and Periods Go--and Why?
To quote the article, universal American usage places commas and periods inside the quotation marks, regardless of logic.
~"Diane," she said, "put the book down and go outside for a little
~"I will in a minute," she replied, "as soon as I finish this
This rule applies even when the unit enclosed at the end of the sentence is just a single word rather than an actual quotation:
~To get to the next page, just press the little button marked "Enter."
The only exception is when that last little item enclosed in quotation marks is just a letter or a number, in which case the period or comma will go outside the closing quotation marks:
~The buried treasure was marked on the map with a large "X".
~The only grade that will satisfy her is an "A".
~On this scale, the highest ranking is a "1", not a "10".