Just tested this by exporting a very small test app with only 2 sprites and a touch event via Construct2 using the Direct Canvas option. The Appmobi "Simulator" has the black screen but when I touch where I think my sprite is located which is using the touch event, the black screen goes away and the app works fine. When I choose the "Test Anywhere" function and load it up on my actual iPhone4 via AppLab, it works just fine with no black screen.
When exported via the "HTML Browser" option in Construct2, the App works with no problems in the AppMobi "Simulator" as expected.