The shorter warranty period compensates for the lower wholesale cost. They way they calculate it, it is a better deal for themselves. Refurb does not mean what some people think. There is no rebuild, it is tested with a battery of end of production line tests which is supposed to identify most parameters and adjustments. It is passes, it is cleaned and reboxed. If it is in need of repair, it is repaired unless the cost of repair would be higher than the cost of warranty support and the lower price received for it. In that case it is probably scrapped.
I had a business for years that was the sole warranty and factory service for a large manufacture of pro-audio equipment. We received pallets of warranty and store returns daily. Those that were not economical to repair because module and parts stores for other repairs. About 50% of all returns revealed no defect and no warranty claims after being "refurbed", boxed and sent out again. These items were similar in prices to the Nikon camera range. I doubt if we got back any where as high a percentage as Nikon does since the typical buyer of this pro gear was pretty knowledgeable about its use. No one was sending them back because they were too heavy or the files were too big. Whether a camera is refurbed, as in "repaired", is probably determined by its sales price. If any real repair is needed on a D3100 or CoolPix, it is probably headed to the crusher. Repair of a camera costs more in labor to assemble on. One tech can align or final assemble new items much faster than a skilled tech can diagnosis and repair a defective one. Stan St Petersburg Russia