Comment 2 for bug 841278

There could not possibly be a "good" reason for this other than a slight performance win.
sb-fasteval doesn't have this behavior.
sb-eval does, mainly out of laziness - it does not check for macro-function (signaling an error), and then fdefinition if not a macro.
The simple evaluator (if no full eval implementation is built in) also exhibits the misbehavior.