Face of James Joyce

Jane Wildgoose alerted me to Lot 197 at Sotheby's English Literature themed sale, described in the catalogue as “the final visage of one of the greatest authors of the twentieth century.” Sadly this was not the actual face of James Joyce, but a plaster death mask made in January 1941 in the hours after the writer's death.  It sold for US $58,401.  The next lot, no.  197b, a bronze cast from the plaster death mask, didn't even make its reserve of US $8,500.  Why was anyone really surprised that the cast made of inferior materials sold for a much higher price?