Most shipments for iPhones and ipads come by air freight not by sea mainly because apple unlike other manufactures build to order and hold only small quantities in warehouses. Considering how many ipads that can be built in 5 minutes it is the most effective way to hit the market. That is why old stock disappears from shelves so quick because inventory control is tight. However retail stores like best buy may hold extra stock but again it is ordered on demand. This also applies to the desktop and MacBook products as well
All shipments for ipod touch, iphones and ipads are from china via hong kong and Singapore . It has been stated Apple's manufacture Foxconn can produce 10,000 ipads per day per factory run x 50 lines in full production This is needed to meet world wide demand. See below info
Foxconn plants china info early 2011
The new plant shall indeed increase the iPad’s market availability. At present, the biggest production unit of the region is located at Shenzhen with a production capacity of 2.5 million iper month. In comparison, Foxconn’s Chengdu unit is expected to reach an output of 40 million devices per month.
Note this is all devices ie iPhones iPod touch and ipads
One more thing......
Foxconn has more than 800,000 employees.and manufactures products for other major companies
Apple is the largest customer for Foxconn
More info
Analysts estimate that more than 100,000 of Foxconn’s 800,000 workers in China are working on Apple products.
Apple also works with Taiwan’s Quanta Computer at plants in Shanghai and Suzhou, where labour costs are outpacing the rest of the country too.