It's not cherry-picked, actually; the historical standard in the UK is three years. However, it's not common to do any qualifying exams or courses in a three year program. There's a new trend of so-called "Centres for Doctoral Training" where students take four years, and get a year or courses and qualifying exams at the start.
Consequently, UK PhDs are often quite a bit more junior than US PhDs -- although it works brilliantly if you're an academic high-flier, as you show up and start doing research on day one, leaving with a doctorate three years later.
Consequently, UK PhDs are often quite a bit more junior than US PhDs -- although it works brilliantly if you're an academic high-flier, as you show up and start doing research on day one, leaving with a doctorate three years later.