Apple has announced iPad availability in the U.S. beginning April 3 for WiFi-only versions and late April for 3G versions. The rest of the world waits until the 3G version ships.
I think Apple's decision to ship beginning in early April after announcing late March (60 days from January 27) is not entirely an accident. When Jobs announces a product in "Spring" he's known to release it so late in the year that he shows a dictionary definition of "Spring" to prove it's still spring, despite that everyone in the auditorium feels it's summer. Pre-announcing the iPhone 3GS so far in advance that existing models' sales were clobbered by the Osborne Effect isn't a rookie mistake, either. I believe that carefully controlling information and disappointing expectations of immediate availability is a deliberate tactic to heighten anticipation and garner both first-day crowds and free press on product release. Apple is into the buzz.
With Gartner announcing in effect a doubling of touchscreen devices over the year, Apple's position as the company folks think of when they think of touch screens is important. Building buzz, staying in the news, and providing a carefully-crafted experience are all part of Apple's marketing and brand management effort.