Just like for the itouch, 3rd party companies make stuff for these devices and I'm sure OPENING up the option for SD slot or USB port would have added more uses for the IPAD. I prefer to use USB port instead of SD slot, since my usb hard drive hold more.
But if no usb at least give me a SD slot so I could import my photos or take with me SD cards filled with stuff I use for work or pleasure. And to allow others to show me their stuff on the IPAD. I guess you can convince yourself you don't need USB or SD slot on the IPAD but really I think you will miss it over time. I know I would have liked to have SD slot on my Itouch or zune. It would turn the IPAD into something that could play all my media on my hard drives. 3rd party apps could do it, just like 3rd party apps do all the other cool stuff on my itouch. And my apps are always being updated.