There is a more modern and more flexible approach to punctuation, especially in this area, as described at http://www.grammar-monster.com/lessons/quotation_(speech)_marks_colon_or_comma.htm (alongside the more traditional and prescriptive approach):
The majority of people do not adhere to the guidelines regarding the use of commas and colons with quotations. Nowadays, it is acceptable to introduce a quotation with a comma, a colon or nothing. In modern writing, the choice of punctuation depends largely on the desired flow of the text (i.e., how much the writer wants the reader to pause).
(The terminal punctuation is not addressed explicitly here, of course, but the freedom allowed to the writer surely holds here too.)
And, from the Dept of Language, Literature & Culture, Aarhus University:
... There is much variation in the ways in which individual publishers punctuate quotes; for example, some treat full sentences that are quoted differently from words and short phrases. The important thing is to be consistent.