I suspect it is a matter of background, as you imply. Twitter has its roots in Rails, and I believe they also use Scala heavily. Both Ruby and Scala use newline

I suspect it is a matter of background, as you imply. Twitter has its roots in Rails, and I believe they also use Scala heavily. Both Ruby and Scala use newline as a statement terminator. GitHub is another Rails shop that avoids semicolons in JS. Zepto.js recently removed the semicolons from its code base, and its author was a core Rails developer.