Just to comfirm, I agree with everything you say above Mike but you appear to maybe coming at it from the wrong angle.
One of the key points of the iPad (according to apple) is apps should be fully functionable in any orientation. If you read the apple speil on making the most of the additional iPad UI over the iPhone/iPod Touch, it goes into great details there.
If you use "cmd" + the left/right arrows you should be able to orientate the simulator. This will allow you to simulate exactly what a user would experience if they start your app in the wrong orientation from what you have coded.
I would recommend you reverse the code amendment you made(shouldAutorotateToInterfaceOrientation - NO) and code your app to display in any prientation. If you must code in just one then I suspect a user will be forced to rotate the device to rectify the issue.
I know you are keen to test your landscape app but I am unaware of any way the iPad Simulator can be forced to start in Landscape without you work around you mention above, which like you have already advised defeats the point. I suspect your stuck with "cmd" + "left/right" arrows.