Creating the dashboard and widgets with both landscape and portrait mode support seems like a real pain. The widgets are not grid aligned like on many competitors, so rotating could cause some confusing moments.
The big thing to me is that there are only 4 use cases that are personally relevant for portrait mode. Phone Calculator Note tablet w/ stylus Music player
ogahyellow, assuming those are the only relevant portrait mode use cases totally ignores one of the greatest devices of the decade, the N95, which ushered in the totally portrait mobile computing we see today. You can do ANYthing in portrait with relative ease and convenience, as the N95 showed.
You might need to research the N95 and N97's rabid user base and find out exactly what can be done in one hand in portrait nowadays.