I'm not really sure why you keep mentioning this side of the pond, as we've already established the difference between American grammatical syntax and the rest of the English speaking world. Nevertheless, I grew up and went to school on the same side of the pond as you, and had high grades in English and literature.
The two different types of grammar punctuation are
British Style (also known as
Logical Notation), and the
American Style, used almost exclusively in the US but also somewhat in Canada. The
British Style is largely governed by Fowler's
A Dictionary of Modern English Usage, whereas
American Style is largely governed by the
Chicago Manual of Style and the
New York Public Library Writer's Guide to Style and Usage (Harper Collins). Most journalists abide by the
AP Stylebook and the
MLA (
Modern Language Association) which both use
American Style in most instances but not all.
The
only major difference between
British Style and
American Style are the placements of the commas and periods -
American Style places commas and periods inside the quotation marks,
British Style places them outside the quotation marks.
Colons, semicolons, question marks and exclamation marks are handled exactly the same way in both styles, with colons and semicolons (as well as asterisks and dashes)
always being placed outside the quotation marks, and exclamation and question marks being placed logically (whether the mark itself is part of the quote, or whether it applies to the entire sentence).
There are, however, several American style guides which are specific to certain specialties, like legal writing, linguistics, and most technical writing, which prefer the
British Style. I know this because I've written published works that dealt with such specialties and had to become intimate with all of the above mentioned style guides.
Oxford Comma (serial comma) usage is all over the place, both here and in the UK. In the US, the serial comma is standard usage in non-journalistic writing that follows the
Chicago Manual of Style. Journalists, however, use the
AP Stylebook which, while not outright prohibiting it, strongly suggests against its usage. In the UK it is standard usage to leave it out, despite
Fowler's Modern English Usage recommending using it. The Oxford University Press sure uses it, though. So does Harvard. They're about the only ones who do religiously, and it's why the serial comma is often referred to as the Oxford or Harvard Comma.
Which way is correct is clearly up for debate, as there is no clear authority of accepted usage to make either correct or incorrect, unless you are writing in the journalistic confines of the
AP Stylebook, or the OUP, or at Harvard. It is, however, universally recommended to use the serial comma to prevent lyrical or musical prosody in the text (a rhythm, stress or intonation of speech which relates an emotional state, sarcasm, focus or emphasis) unless such prosody is what you are after. The use of a serial comma to prevent prosody breaks up the individual words and reduces ambiguity or confusion in some cases. So the general consensus on the serial comma is that there is no consensus. If you want to use it, use it. If you don't, then don't.
Here's
an article written by an American English teacher who fervently deducts one point for every period or comma that's in the
British Style, outside of a quotation mark. It'll really chap your cushions.
I may very well have misspoke in saying every Web site that deals with the grammar of American English contradicts what you are saying. I'll concede that point. "Every Web site" is a little on the absolute side. However, I have yet to come across a single one that agrees with you, and it's not for lack of trying. So, please consider my remarks amended within that context.
In a nutshell,
this page from Purdue University gives an excellent overview of the general rules of when and where to use quotation marks in American Style English. The rules coincide with the accepted style guides of American English mentioned above.