First of all, Apple is selling so many of the iPad devices that it tends to delay it's announcement of the iPad 2 as it would lower down sales of the original iPad as hence the crowd would opt for the next-gen device.

Secondly, Apple could also possibly secretly waiting for the launch of Motorola's XOOM Tablet that would feature Google's Android OS "Honeycomb" specifically designed for tablets. This would definitely make Apple rethink their iOS strategy and thus release and price their upcoming iPad 2 accordingly.

Although the XOOM is not out yet, but Verizon and Motorola itself is planning to announce it very soon.

As of now, word on the street is that Apple, is planning a special iOS launch, while announcing their iOS 4.3 update, they might possibly unveil the iPad 2 along with it since these both are product refreshes. Also, due to health concerns, Steve Jobs wouldn't be there at the unveil himself in front of the crowds.