Unit shipment not telling of whole story
It would be pretty naive to base the success of a company purely on unit shipments. Let's take a closer look at WD and Seagate's quarterly performance:
Units shipped: WD: 51.1M, Seagate 50.3M
Revenue: WD: $2.6B, Seagate: $3.05B
Net Profit: WD: $400M, Seagate: $518M
Profit Margin: WD: 25.2% Seagate: 29.6%
Now if you were a business, which one would you rather be? IMHO, Seagate is more successful at carrying business, and still #1 disk drive company as far as the ability to maximize revenue and profit margin. Unit shipment is just for bragging rights, and that's where the perceived numerical advantage ends. WD is shipping lots of cheap low capacity units into the retail markets, and that's how unit shipments get to be higher. Those products are easier to make due to better yield, but don't provide a very high profit margin. Rating a company purely on unit shipment is a pretty shallow and lob-sided way of looking at a business. What really counts is the overall business model, and in that aspect, Seagate continues to shine.