Sounds crazy, but clearly there's reasons for such a strict agreement from both sides: developers really want to get a head start on what will surely be a huge market for apps and content starting on the iPad's release, and obviously Apple wants to make sure that the device stays under cover until it releases. You might think that they'd actually benefit from a little exposure, but don't forget: this is Apple -- they depend on the hype and interest that secrecy before release creates. After it comes out, seeing the iPad out in the world will likely sell even more units, but pre-release, Apple's customers are happy to stand in line to be the first to use the iPad.
Of course, this is all from anonymous sources -- it'll be interesting to see if any of these "iPads in the wild" find their way out to the public in the form of pictures or video. Until then, the rest of us (including many developers who've played big parts in building up the App Store to where it is today) will have to wait until April 3rd.