[mkremins]

I've never seen any explanation from Rich on the subject, but semantically speaking, vectors used in syntactic constructs are almost universally meant to denote binding forms. Let-bindings, loop-bindings, function parameters and the like all use vectors in the context of binding symbols to values.

I find that, having gotten used to the mental shortcut "square brackets == binding", the distinction makes it easier to read the "shape" of code from a very high level and get a general understanding of its meaning at a glance. YMMV.