Not familiar with the 737, but am I to understand there is no cabin altitude master warning caption or EICAS message complimenting the aural warning? If not, then while the Helios crew didn't exactly cover themselves in glory, I would consider inadequate design of the pressurization system by the manufacturer to have been a significant contributing factor here. Similar in consequence to the inadequately designed AT retard function which contributed to bringing down THY 1951 at Schiphol.