I'm confused about something. Is whether or not to use a comma inside or outside of a single quotation mark - be it within double quotation marks or simply for quoting a title - merely based on an American versus British style, the former using it on the inside and the latter on the out?

This is how the British commonly punctuate such things:

"I once tried to read ''War and Peace', which my English teacher had recommended," said John, "but I found it boring".
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I had a look in the COCA and typed:

, "

It shows lots of examples of commas being inside.

He's got me. I start ticking off shows I watch regularly: " Seinfeld, " " Homicide , " " NYPD Blue, " " The X-Files, " " ER, " " King of the Hill "... I quit at around 11. Maybe six, seven hours a week, excluding sports, newsmagazines and " Rivera Live. " # " You can rattle off more good shows than the average viewer wants to watch, " he says.
Okay, so it is an American vs. British thing, then, rather than a really regulated grammatical one, I guess.