Well aside from the OS differences there are screen differences. Also going with Android there are going to be a lot more choices of hardware, you have Dell Streak 10", LG Optimus, Toshiba, Samsung Galaxy as well as the Xoom, rumor is these should be released this Summer.
Just comparing the Xoom to iPad2 there is the screen size 16:9 to 4:3. Some folks like the 4:3 aspect ratio. I've gotten use to the 16:9 and prefer it, esp for a 7" tablet.
As far as the market, most major apps exist on both platforms even have versions for the BlackBerry platform. The only major app I can think of that exist on the iOS and not Android is netflix. Also for niche apps there is also a direct equivalent. For instance GoodReader is an excellent full featured PDF reader/editor. For android it would be RepliGo and ezPDF.
The one area in the market where iOS is beating Android is in complex games like Unreal and such. While there are many making their way to the Android OS many are not.
On the flip size there are much more free games on Android than on the iOS.
As for reading apps at the moment iOS and Android are on the same footing. However as you pointed out this might not be the case in the near future. And if that happens Android will be the clear leader.