Two years, that's regulated in law. Very few companies offer anything better than that, and especially not any manufacturer of consumer goods. But as I tried to explain, a consumer here has the right to expect a product to last longer than that. The difference is, after the two year period, the consumer is obligated to prove that there was a fault in the product not caused by wear, misuse etc. Hardly anyone ever does. During the two year warranty, the opposite applies. The manufacturer has in theory the right to try to prove that you caused the fault, but that rarely happens unless there's something obvious.
I can't see how it would be because of HV, since there are exposed mains traces everywhere. Moisture (and dust) ingress? Could it act as a heat spreader to nearby copper fills, or would it be less efficient than just leaving them open to the air?