Plus their are tons of clauses in insurance that they can use that when it breaks you get NOTHING. Not a replacement, not money, NOTHING. ESPECIALLY with stuff like a miner. Most likely they will send you a letter stating "We hate to see that your item broke, however we do not typically insure this type of item as [insert excuse here about overclocking, heat damage, etc]. Since this is not an item we would typically allow to be insured we have provided you a refund for the $42 you paid to insure this item." This is something item insurance will frequently do is just give a refund for the price paid for the insurance.
I know this is pretty much standard in UK probably all of EU law. There is a reasonable argument for fair wear and tear whereby even after insurance coverage the item is not replaced as it is judged to have been used and expired in the natural course of fair wear. Even if replaced in 4 years this item wont be of any worth, their liability at that time is to provide an item of no worth. Of course they will opt for cash in this case to save even spending on postage and the cash value of something nearly worthless is a few cents I guess.
Alot of modern insurance sold to consumers is legal and fair but not worth the bother. I know someone who paid 70 a year for washing machine cover, after a few years they spent almost as much as the washing machine costs anyway. Just not competetive, if this cover was 20 or less maybe it would probably still be a profitable enterprise for the company. Most of money spent goes to administration and fraud prevention. They naturally go out of their way not to pay any more then required, they are obliged to do so as a profit making enterprise.