I think it's ridiculous that ANY company could have plenty of stock which clearly wasn't in danger of goin out of stock any time soon and them not offering a replacement from their stock.
I suppose one of the issues is that warranty replacements aren't always full retail products and aren't always even new (refurbishments).
If the retailer sent out a replacement from their stock what do they do if they get a "brown box"/refurbished replacement from the manufacturer?