No Common Sense
"I stressed that I often leave my laptop charging overnight under the sofa on the carpet"
Lets see - insulate your laptop with carpet and a sofa whilst on charge, like any laptop (or computer for that matter) it gets hot, it should be placed on a firm surface (like a desk) to allow airflow to all areas - thats why it has feet! I can understand the reason to hide it and that it might fit snugly under the sofa. Its akin to placing night lights on a plastic bath and wondering why you end up with a house fire.
So you slowly cooked your laptop every night and wonder why it failed bit by bit, you ignored the case going yellow and the screen failing and it appears it eventually melted internal wiring causing the power lead to eventually over heat and short out. Surely you notice it was hot when you removed it from under the sofa?
I guess your house doesn't have rcb's otherwise it would have popped them long before you got injured.
No wonder its a nanny state these days, some people have no common sense.
All I can say is RTFM... a few excerpts from it.
Important: read all the installation instructions (and the safety information in Appendix B....) carefully, before you plug your computer into the wall socket.
remoce the power cord, battery etc if :-
you suspect your computer needs service or repair
The power adaptor may become hot.....Always allow adequate ventilation around the adapter....when possible place on a hard surface to dissipate heat.
...it is normal for the bottom of the case to get warm...place on a flat stable surface...
the bottom of the mac is a cooling surface that transfers heat.... is raised... to allow airflow....
Warning: Do not place your Mac on a pillow or other soft material when it is on
Sounds like Apple did everything they could except suggest that you shouldn't be entrusted with one of their products as you clearly aren't capable of operating it correctly (or any computer for that matter). Apple could have said hard luck you did not follow the instructions in the manual instead they sorted it out.