'Gotten' is surely standard USAnian?
Five ways the internet era has changed British English
Anyway, it's just saying written UK English has become more informal. I would think that's because of online forums, social media, blogs etc being more chatty. Pre-internet, published informal texts would be much less common, maybe almost non existent.
A fair whack of "Americanisms" come from Scottish Standard English or Hiberno-English
Gotten is perfectly legit here as it is the past-participle of "get" in Scots, SSE is modern English mangled with Scots and Gaelic, Scots is of course middle english mangled with Gaelic and then presented to a different set of trading partners from what middle English and Northumbric were.
See also Halloween.
British English is a fallacy created by the ruling class to attempt to present the UK as a single homogenous thing rather than the inherent multi-cuktural thing it is, feck Scotland has 4 distinct high-level cultures as it was (lowland, Highland, hebridean and norse), England has an imperial fuck ton of them, as can easily be seen by putting a Geordie in the same room as a Cornish.
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