Matt, The Mainframe business is low revenue but high margin business and you will pry it out of IBM's cold dead hands. It is a no brainer for them to keep pushing as they have 80+% market share and a captive audience as the path to move off a mainframe takes YEARS.
Erik, Yes the whole DS, DCS and N Series range are OEM'ed from NetApp/LSI and that is why they will go, the StorWize range is resigned to replace them, the new V3700 is the box to replace the DS3500 as the V7000 replaced the DS3950/DS5020 and the DS5100/5300 ranges. The only product from that line that might survive the end of the year is the dense DCS3700 for Video etc.
IBM will get rid of as many OEM'ed systems as they can, they want to own their storage destiny and they have either acquired the products to do it (XIV, TMS) or built them in house (StorWize, SONAS).
HP are doing the same thing of out with the old (EVA, P2000/MSA2K, P9500/XP) and in with the new (StoreServ 7000/3Par, StoreVirtual, StorEasy).