Eastern and Western Kassadin Builds

Kassadin has been seeing a decent bit of play recently on the pro scene lately. I've noticed that in almost all of the NA/EU Kassadin games they build luden's echo (or buy the components to build into it) and that only Ryu hasn't built it in his Kassadin game. On the other hand the Chinese/Korean Kassadin players don't build luden's echo at all. So I've been curious if this is just due to regional meta differences or what the pros/cons are for different regions opting to build/ignore luden's echo on kassadin.