Dragonborn form Argonessen? Well that's to be expected. Granted they already detailed Argonessen in the last edition but it really makes sense.
3.5 Dragonborn, however, are *vastly* different from the 4e variety, so the ties are tenuous. Remember that 3.5 tieflings in Eberron were from the Demon Wastes, not Sarlona.
I don't think Dragonborn changed all that much from 3.5 to 4e.