The design of video calling is the brain-child of Rob Maison, a recent graduate from England that arrived at Facebook last October. He worked closely with Zuckerberg (CEO) and Cox (VP of Product Design) on this product and agreed to make the experience as simple and uncluttered as possible. It is this simplicity that they expect will make Facebook extremely popular with the large untapped market of potential users who have no prior experience with video conferencing and who may even feel overwhelmed by it. Simplicity, in this case, means getting the job done, no bells or whistles!
Meanwhile, Google+ is downplaying simplicity and betting that their Hangouts, with all their features and options, will resonate better with their users whom, it would seem, they are assuming will be savvy enough to use and enjoy them. Although Hangouts are easy to use and intuitive, they were born from a different design philosophy.