Apple decides to launch their products based around PR.
They are in the process of deciding whether to launch the iphone 5 in early June/July or hold off until fall. Either way, they have to keep mac lovers entertained so they are launching the white iphone4 and other new mac products.
“Apple is a company that thrives on PR excitement…and the big hole in the update schedule before the iPhone 5 arrives could damage sales. Hence Apple seems to be ready to release a barrage of new hardware, including the white version of the iPhone 4, to keep everyone’s pro-Apple sentiment topped up.”