Everyone over on Sodahead is eager to defend “the rules of grammar”, and oh how it does the heart good. The trouble, of course, is that there is not now, nor has there ever been, a definitive authority on “correct” English grammar. You can point to Strunk & White or Brown, but neither are universally adhered to by anyone.
And because people tend to invent rationalizations for their preferences you can find British grammarians who will eloquently and exhaustively explain why the terminal punctuation belongs outside the quotation marks, and American experts who just as eloquently and thoroughly explain why it does not.
The reality is, English is parsed by people, not by CPUs. It needs to be clear, but it needs to be varied and interesting, and it needs to connote and imply. It needs to gamble and flirt and occasionally betray. As in any other artistic endeavor, we must understand the rules, but then we must break them. If we were unwilling to do so, we would all still be speaking Latin (or Aramaic), we would know neither Falkner nor Shakespeare, and we certainly would be impoverished without the tintinnabulation of the bells, bells, bells, bells, Bells, bells, bells.
And who would wish to live in such a world?