If you look into detail on those warrenties, most are a insurance policy, that a seperate company writes for said company, and, there are stipulations a mile long. Plus, it only covers a percentage of the original purchase price. For exapmple, the policy will cover up to say $4000 or $6000. If they can FIX your engine for that much, as long as the claim is approved, then your good to go. If not, then, there is gray area, and it would be up to the engine shop to eat any additional money involved. And trust me, YOU the customer, are paying for this warrenty/insurance policy. Not the shop.
I think to many guys think that warrenty means, I can beat the living death out of my new engine, and, if it blows up, I call up said engine shop, and they say, " Oh shoot, you broke her huh? Ok, we will ship you a new one, have a nice day". NOT. Most times, its simply a meaningless, worthless empty promise, used as a marketing ploy, to get you to go to them, instead of somewhere else. One of the biggest jokes in engine warrenties, is the GM crate engine warrenty. Good luck getting anything out of them.