[plt-scheme] square brackets on cond procedures?

R5RS does not show square brackets around (cond) ... why does HtDP use 
them? How does their meaning differ?

R5RS:

     (cond ((> 3 3) 'greater)
           ((< 3 3) 'less)
           (else 'equal))                   ==>  equal

HtDP:

(cond
  [(<= n 1000) .040]
  [(<= n 5000) .045]
  [(<= n 10000) .055]
  [(> n 10000) .060])