I had read somewhere else that this was an intentional thing. When you are looking at the home screen it is supposed to be easier if you are in portrait mode than in landscape mode. But if the keyboard is out it is forced to switch so you can read stuff.
I do think this is something they are changing though, a simple feature such as auto-rotate should work on the home screen. It's not like the home screen can't rotate, it' just not set for auto-rotate, which would be a very simple fix.
may cause a problem when a call comes through. That was a big issue with the Storm. Screen would freak out and the user would have to chase the "answer key" all over the place. (the hard send key didn't always work)
Maybe the OS can't handle all that info at once so they left it out? I don't know.....
I don't care one way or another though. I've adapted to it.