Another example, the BBC Series the Bodyguard (a different concept but similar enough) or Israeli Homeland vs US Homeland. The US has made the mistake on a number of times of taking a great concept and dragging it out too long. Maybe one of the few that was justified was House of Cards, where the longer US version was (arguably) better than the UK version...
The US version of The Office is apparently by far the most watched show on Netflix (US). Even if you acknowledge it went on probably one or two seasons too long (which isn't an uncommon opinion, to be fair), 7 seasons is far longer than most BBC shows last.
And, as another poster noted, I would argue that a lot of people think the BBC version of Sherlock has definitely gone on way too long.
I think British TV has actually started taking influence from American TV over the past decade or so (or at least realized that Americans are watching and have started to cater to those audiences). Downton Abbey I feel also similarly went on probably a couple series too many.
BBC being funded by tax payer's money compared to US for profits company where they have incentive to not cut off their series with many viewers?