Atom outclasses s370 in performance and power consumption. But until Atom came out, for a NAS or low-demand server a s370 was significantly superior to p4 for that type of work. Cheaper, lower power, silent. It's a knock on phenomenon. Lower power means cheaper to run means cheaper PSU plus passive cooling means quieter means benefits all round.
However, now that Atom is launched and an all-in-one mainboard can be had for around $60 for the Atom 330, it really is time to kill off s370. You can bet NO MORE ARE BEING MANUFACTURED, but these are old stock sitting on shelves.