Notice that there's no comma before that "too"? Sure, it could be an oversight. But because I'm seeing more and more cases like this without the comma, I doubt it.
Plus, the very next day, the New York Times reported in an article about India that "books and plays have been banned too."
The comma-less "too" is outnumbered in the New York Times by their with-comma counterparts by perhaps a 10-to-1 margin. But that's still 10%.
We see the same thing going on with "either." Both the New York Times and the Los Angeles Times occasionally eschew the comma before "either."
"I can't imagine Janet Nguyen thinking that would be worth it for her either," a Los Angeles Times reporter wrote.
And another from the New York Times: "Gestures didn't do much good either."
I wanted to get to the bottom of this. But a funny thing happened on my way to learning why these commas are going: I realized it's totally unclear where this comma "rule" comes from in the first place.
My style guides contain lots of very specific instruction on the use of commas in very specific instances. But none address commas before "too," "either," "anyway," etc. at the ends of sentences.
Here, however, are some rules from which we might take some guidance.
"Nonessential phrases" are usually set off by commas, many of my books tell me. So, "My laboratory mice, the little darlings, gobble up that saccharin." The phrase "the little darlings" is not essential in understanding the rest of the sentence (for those keeping score at home, yes, it counts as an "appositive").
So does "too" constitute a nonessential phrase in our examples and, if so, is that we usually put a comma before it?