Alef:
To take this to a higher level, I might mention that in 2008 "The Language Council of Norway" changed correct usage from
Norway has a language council, but none of the English speaking countries do. Which is why English is such a weird language with so many word borrowed from so many sources.
TheEnglishMaster:
Punctuation is not subject to rules, merely 'conventions' ("a set of agreed, stipulated, or generally accepted standards, norms, social norms, or criteria, often taking the form of a custom," says Wikipedia). The logic of these conventions is dictated by what's easiest for the reader to decode. The convention in the punctuation of direct speech is to regard the dialogue tag ('she said' etc) as part of the same sentence as the direct speech it's attached to, hence the use of a comma.
I agree with most of what you've said, but can't get my head around the logical flaws. For example, here's one side of a phone call.
"He's coming home now. He's at the door. I think he's really going to spank me!" Sally exclaimed.
"He's coming home now. He's at the door. I think he's really going to spank me?" Sally said, unsure if she actually thought he would go through with it this time.
"He's coming home now. He's at the door. I think he's really going to spank me." Sally said.
Three complete sentences in quotes. We all agree that the first two examples should end with either "!" or "?". (Quotes had to be used because ?. just doesn't work). I just don't see anything inherently different in sentence three to use a "," rather than the "." that ends all of the other complete sentences. Now if a sentence is being being split, say:
"I still love you, but you can never use that paddle again." Jane moaned as she rubbed her bruised bottom.
Became
"I still love you," Jane moaned as she rubbed her bruised bottom, "but you can never use that paddle again."
then I can see that it's one sentence separated by the identifier as opposed to being two complete sentences, which is a different thing, but sentences end in complete stops, question marks, or exclamation points.