Yes Clemens has the lower ERA, but I think this award can still go to Carpenter without too much fuss.
This year Carpenter has 7 Complete games, 4 of which are Shutouts. Clemens has 1 Complete game, no shutouts. Per game pitched this year, Carpenter on average pitches one inning more per game.
Also, Carpenter has a better K/BB ratio than Clemens along with 30 more innings pitched (roughly). So yes a 1.57 ERA is fantastic, but Carpenter has some great supporting statistics too.
...Boston papers now and then suffer a sharp flurry of arithmetic on this score; indeed, for Williams to have distributed all his hits so they did nobody else any good would constitute a feat of placement unparalleled in the annals of selfishness. -Updike