Are you sure it's that narrow? I was under the impression that they can also refuse a claim (or void your policy) if you failed to disclose something that would have increased your premium. For example with your home insurance - if you fail to disclose that you have been burgled 5 times in the past 5 years, you would get a premium that is much lower than it should be. If you then claim and this failure to disclose comes to light, my understanding is that they can refuse the new claim, even if the new claim relates to something completely different (e.g. if the house burnt down).
It's also very hard to be black and white about what medical history is relevant. Ok, breaking your wrist 20 years ago is not likely to be relevant to sudden death at the age of 37. However, serious infections can lead to long term organ damage, which in turn can increase your risk of all sorts of things. As it happens, my wife was hospitalised with a severe infection 2 years ago, and we recently discovered that a number of life insurance companies won't even provide a quote for cover because of that (even though she has thankfully fully recovered). I believe this is especially the case with the mass-market low cost insurers, as the way they keep their costs down is by only covering very low risk people.