I think it depends on which Nomad you're talking about. If the 30GB is the type I'm thinking of, then I'd guess that the price difference has to do with size. The Nitrus appears to be aiming at the iPod-sized player, while the Nomad (again, if it's the one I'm thinking of), is the size of a discman.
Nitrus
*edit*
Hmm, well I see the product you're talking about. I assume you're speaking of the 30GB version of
this?
On first glance, the Nitrus appears to be much smaller. So my best guess would be that the storage technologies are different.