both the m8 and m7 have black bars because they are both metal phones. if there were no bars the metal would act as a faraday cage and you would get terrible reception. every iphone has them too and apple wanted to remove the bars but they couldn't. htc decided to integrate the bars into the edge of the display but unfortunately it has convinced people that they are just stupid and cant design a phone as this thread shows. so you can have no black bars, or you can have a full metal phone, but not both. that is why the note 4 and galaxy s models have no bars.
And it's the evolutionary design with the 20mp camera. Funny how they discussed low light performance on the front camera but not the back.
And honestly the black bar explanation might have worked 2 years ago, but the iPhone as well as the new A5 and A7 show you don't need to have this type of bar anymore. Back bars like the One and IP6? Ok - it is what it is. Adding another substantial one to the front? So 2013.