Basing the decision strictly on this one point, I have a hard time understanding it too, at least in my circumstances.Reading that, I cannot understand why anyone would choose DiveAssure.
If I had "something official from a licensed instructor working with a recognized training agency that I had received training for and had demonstrated the skills necessary for a dive to a depth of 40m/130ft" (a long-winded way of a single word starting with "c" but choosing my words carefully to avoid misinterpretation by some) that I could show to a dive operator or insurer then it would be a moot point - I would be covered below 30m/100ft. But I don't, and the response from the customer service agent made it clear that the only exception would be if I were actively in the process of receiving said training or demonstrating said skills when the dive accident occurred.
That raises a number of questions in my mind - I'm imagining a scenario where I'm diving with my also-AOW-certified buddy at 29m and her BCD suddenly blows out and she starts sinking. I go deeper to chase her to make sure she can work through the problem - we go down to 32/33/34+m before I can catch her and we work through it and get ourselves safely to the surface with all the necessary stops. But I incur a DCS hit in the process anyway and need treatment in a chamber. Am I covered? I don't know for a certainty that DiveAssure would deny my claim - insurance adjusters definitely have latitude and in this case they might decide to pay it out anyway even though "technically" they might not have to. But based on the strict wording I also don't know that they wouldn't deny it, and that definitely is a red flag for me.
However, at least for divers living outside of the US and Canada, it seems that DiveAssure has much more generous benefit limits than DAN does - four times as much in some categories. For some that might be a reason to choose DiveAssure over DAN - accepting the risks of the depth restriction in favor of the benefits of a higher payout. Or, judging from past posts on ScubaBoard from members living in Quebec, Canada, at least at one point not long ago DAN could not provide insurance to members living in Quebec (not terribly surprising - there is a long list of things especially when it comes to anything remotely approaching legal issues where the laws in Quebec are wildly different from the rest of Canada, with a huge impact on a wide range of consumer products). A diver living in QC would have no choice but to choose DiveAssure over DAN at that point in time for dive accident insurance needs. (Side note - that appears to have changed now. DAN Canada's FAQ now has a line that specifically says "DAN World is now able to offer membership and dive accident insurance to Quebec residents.")
What I honestly dislike about DiveAssure International is that on the surface they say that there is no depth limit (see the wording on the Diving Insurance page under "Depth Limit") but when you drill down into the specifics of the Terms and Conditions you see that isn't actually the whole truth. Intentional or not, that is very misleading, and makes that red flag I mentioned that much larger and brighter.