This is a deliberate design decision in CoffeeScript – "everything is an expression" (see http://coffeescript.org/#expressions).

This is probably as a result of CoffeeScript's Ruby-esque syntax and semantics. It does mean you can write some very clear and succinct code at times, but the tradeoff is that it can have unforeseen performance implications.

It's what ruby does and coffeescript is basically an exercise in making js more like ruby.