I talked to an engineer from Sensirion (the makers of the temperature sensor on the S4) a couple of weeks ago. He told me that the waterproofing was the reason that they couldn't include their sensor in the S5.
Conflicting information, I just talked with someone from Sensirion who was quite central to the the SHTC1 project, he confirmed it was NOT the waterproofing that was the issue and pointed out there are Japanese devices with the same chip that are waterproof, even to IP68 (2m depth).
