I doubt Apple employs the technique by intentionally limiting available product, but instead merely takes advantage of product selling out.
Some people do not understand the technical issues with ramping up a new product, like the iPhone. There are first issues assembling all the new components en mass as well as assembling the final device. Many of the manufacturing issues get ironed out over the first few weeks of manufacturing. New issues sometimes pop up.
Moreover, companies also have to be conservative in managing initial supply to match demand. Apple had to take a 250 million write off over lack luster sales of its very cool but expensive Cube. Companies like Blackberry, HP, and now perhaps Microsoft misjudged initial demand and had to take losses.
Because this is what the SEVENTH phone they are launching and still haven't figured all the details out?