The iBooks app for iPad including Apple’s iBookstore will be available as a free download from the App Store in the US on April 3, with additional countries added later this year.

This is from Apple's latest release that you'll find in our NEWS section here.

I think it's a wrong assumption that it won't ship on the device.... I think what Apple is saying is that you will be able to download it for the iPhone on that date

I'm sure Apple will have other default apps that we didn't see at the introduction, app store, itunes store etc... they all have to be re-written to take advantage of the new screen real estate.

Time will tell, but I'll bet ya it will be on there. They want people downloading books A.S.A.P! Also don't count out a free book or two on there to start!