HDC, I can't explain the difference.  But to drill down a bit on EMC  and NTAP I gathered the following numbers:
  Their price charts track one another and have for a while.
  techstocks.com.
  EMC is promising a NAS solution, but many believe that promise is a  year from fulfillment, making it appear as FUD. NTAP's storage  capacity is expanding rapidly as they implement sophisticated, high  availability clustered configurations over fibre channel. Thus NTAP's  capacity is intersecting with EMC.  My industry contacts say that  NTAP's price/GB is substantially lower than EMC, though this is  certainly not the only competitive metric.
  EMC's new software initiatives for storage management are very  forward thinking and fit the SAN model well.  What is interesting,  and NTAP plays this card, is that NTAP filers can attach to the back  end of SAN networks to serve as storage "devices" in a SAN network.
  My money is in NTAP right now and not EMC.  I pulled out of EMC when  the DGN purchase was made.  (I put the money in the COMM-IC basket  of PMCS, JDSU, CNXT.) If I had more cash, I would probably take a  position in EMC "at the market".
  Here are some financials that I just gleaned from numerous sources  for a comparison.                                               EMC            NTAP  Rev last year($MM) $ 3,974          $ 289     Market Cap ($MM)  $ 72,689         $ 4,989    Price/Sales          18.3x           17.2x     Profit Margin        20.0%           12.3%   Return on Equity     27.5%           12.8%    Sales/Employee     $409.66         $438.51    Debt to Equity        0.1%           0.0%   Return on Assets     17.4%          10.3%
   Gross Margin         55.8%           59%  Revenue Growth rate  36%             80% |