-- I really think this is an important question and, as Justice O'Connor points out, if we have to ask what's the most plausible explanation for this rule, to reward existing vested interest or to stimulate former new works, it seems to me that it's probably the former.
Justice O’Conner thinks the rule favors stimulating former new works 
( z1 think :ARG0 ( z2 person :name ( z3 name :op "O’Conner" ) :ARG0-of ( z4 have-org-role :ARG2 ( z5 justice ) ) ) :ARG1 ( z6 favor :ARG0 ( z7 rule ) :ARG1 ( z8 stimulate :ARG0 z7 :ARG1 ( z9 work :ARG1-of ( z10 new ) :time ( z11 former ) ) ) ) )