The difference here is this is coming from Samsung, given to a prominent Korean newspaper. Based on history, this is better than rumors that start from many techblogs, salesmen, carriers, and strip mall kiosks where someone talked to an employee during their lunchbreak. Samsung is very forthcoming to the Korean media, this isn't Apple being tight-lipped, full of anonymous sources that we, as readers, can't trace. This is a prominent employee, on record, being quoted.
I'll use different speculation, to speculate more. The biggest change, cost wise, I'd guess would be the battery. 4,000 mAh would bring a larger cost change than the screen change, the LCD is a more common tech.
While I know a 4" SAMOLED would be very costly for a competitor to use in their device, if Samsung sold them, costs are different. Costs shouldn't be much different to produce a SAMOLED as an AMOLED, because it was the R&D that changed a production process, but didn't really increase the cost to produce. The 7" lcd can be very similar or even priced the same.
Other small changes, a more expensive wifi chip and a cheaper rear facing camera.
Galaxy Nex running AOSPA
Galaxy S, SHW-m110s, Korean version