Periods separate sentences while commas separate clauses, generally speaking. That's how I was taught and that's how I parse English when I read it. Linguistically speaking, ""I think this rule is correct," he said." is one sentence, and placing a period within the quotations ends the sentence. Personally, I sometimes/often leave out the comma because it does, practically speaking, imply a pause to many readers (including myself), even though all it truly does it separate the quoted clause from the actual verb phrase "he said". I'm surprised no one brought up the way that many European countries/languages write quotations: << >> except they're small sideways carrots or something (it's one symbol, not two; this is just the closest I can get with my English keyboard). And they usually hit enter, so each new speaker or each new "paragraph" of dialog gets a new line with new << >> marks.
The Oxford comma is what follows the final item in a list, and in my opinion is important. Without the O-comma, a list appears to actually be an independent clause and another clause (that I don't know the particular name of). The sentence "It looks like a dick, long and hard" is ambiguous if the O-comma is absent. Is "long and hard" a clause that describes "a dick", or are they two parts of a list describing "it"? Reread it as "It looks like a dick, long, and hard". Ironically, this example is naturally a bit awkward because the first item in the list is a noun while the other two are adjectives, but it works well enough to prove my point.
"Bending the rules" confuses communication in both instances. However, knowing when and how to bend the rules is just as critical as knowing them. Knowing when to use polysyndeton (run on sentences) and asyndeton (lots of punctuation) can stylistically speed up or slow down the "flow" of a piece. Polysyndeton commonly uses lots of "ands" and/or "ors" (this was a fun sentence to write, lol). Most readers view it as expressing excitement or anxiety ("he could like it or not like it or love it or hate it or think I'm desperate or think I'm clingy or think I'm sexy or...") while frequent commas in this case (asyndeton) would read more as if a character is blandly reading off a list. "Bending the rules" here is actually a native, intuitive convention of English that serves both a practical and stylistic function. Semantics rules the day, until you learn that pragmatics dictates semantics behind the scenes.
Edit: I totally switched poly and a. I fixed it once I realized.