An interesting comment but which is not connected directly to english IMHO. I am a french living in Madrid, Spain(14 years already), and previously
had been living in Michigan (7 years) and Southampton (1 year).
I think on the average that british people were using a larger (and more precise) vocabulary
for daily activities (meaning taking out specialized contexts).
But the average american daily vocabulary was much poorer about equal
I would say with the spanish or french "daily vocabulary".
Maybe the continuous rise of the use of specialized "slangs" borrowing lots of english words means
in the long run an impoverishment of native non-english "daily word pools".