yeah, I was noticing that too.
Hero4: 41.0mm height, 59.0mm width, 29.6mm depth (from GoPro web site)
Hero5: 42.6mm, 62mm, 33.7mm (rumored- camera only,) These rumored specs don't match when compared to the Hero4.
I guess the Hero5 is slightly larger because the camera case is waterproof now...