I would add that in addition to the "Lord of the Flies" design choices that must be made when creating a mobile app that these experiences are experiences. Not only are you simply navigating through your options, but you are interacting with them. I would argue that the experience of swiping, zooming, and panning allow the user to get up-close and personal with their interactions. That having been said - and especially in the case of eBay - it's really nice to have an auction (or search) open in one window while researching the widget of the day in another.