I think the Actioncams will go a lot deeper than that- they're pretty rugged. Manufacturer is probably acting on the cautious side to limit warranty claims.
Should be popping out the 'eye-pod' watertight casing castings for the little 808 keyfob cams this week. This is a small teardrop shaped (think of a chubby Albacore) enclosure designed to house the miniature cameras you can get off ebay which offer up to 720P HD for about 25 nicker. Standard definition cams are well under a tenner, but the HD model is well worth the extra moolah IMO. I've used them extensively on model aeroplanes, as they only weigh about 15 grams. The 'eye-pod' will make them waterproof and as the enclosure is more streamlined than the ATC cams and also has a much lower wetted area, it should work well on smaller models where the ATC can be a bit of a drag- literally. Bang goes the theory, we'll see how it holds up in practice.