Janney: [en.wikipedia.org]

Starting around the 1960s, Australia began converting to US style knuckles, and New Zealand is currently in the process of doing so. According to the article, the US style coupler has been making inroads into GB and Europe. One thing knuckle couplers can't do is maintain the alignment necessary for the automatic coupling of train line wires, which is why there are the O-B Tomlynsons, Westinghouse Hs (PE), and those other strange looking ones (BARTD, etc).

One thing the link, screw, and buffer system does is eliminate slack, which US-style knuckle couplers can't do (including the HT variety), even when the cars are equipped with [US style] buffers.