Yes, it is licensing and (quite strict) certification. You'd need to get through fairly good amount of algorithmic and hardware design work on mobile to pass the certification test though, it is far from being a money question only.

One of big issues in mobile imaging is level of parasite heat you would get around sensor. 10C increase in surrounding temperature would bring your noise level up dramatically. And getting temperature raise is easy when sensor is active -- a typical video or photo recording exercises sensor, CPU, RAM, and storage continuously which dissipates heat. 10-15 minutes and your device will be hot to feel. Same with long calls. It is always a battle with laws of physics and product constraints.

Part of Zeiss certification is set of temperature tests when device is put through high and low temperature modes. Think of Middle East or Sahara outdoors usage or Arctic subzero exposure.

N900 and N9 did pass Carl Zeiss certification. Of course, it is not heaven but the certification gives you some assurance on quality under slightly abnormal conditions -- as much as it is possible to use a phone in those conditions.