Just playing devils advocate here, but maybe GW has changed the "theme" of the new Necrons from lets say an Egyptian style to a Pre-Columbian Aztecian style? Those ornate Necron lords looks like they could fit in with the Warhammer Lizardmen!
Hey, in Dawn of War (GW inspired anyways) the Necrons were building obelisks for strategic points. Obelisks where not only Egyptian but other cultures built them too.
Maybe someone could get the info straight from GW?