I disagree. I think it's exactly right, because this isn't a phone or an iPod. You're not going to take it out of your pocket to do a quick calculation. If you need a calculation, you'll already have the thing out and be working on it--so you can use one of the many alternative routes, like typing it into a google search bar, or iWork, or etc. etc. While the Dashboard on OSX is fun and made for a great launch demo, it gets *very* little use by most people except for checking the weather--precisely because bringing up these weird little things in their own little ghetto is a jarring and unnatural experience. "Widget" apps like a calculator on the iPad would be a lot closer to that Dashboard stuck-in-the-middle-doesn't-quite-fit-in thing than the equivalent iPhone/Touch apps.
Tell that to Android which has accomplished the widget use very well. It is one of the highlights of the system. Apple should have been prepared for this. I will buy an Ipad, but I'm waiting for 3g so I have time to hope...and see.