As far as I'm concerned, Sony has a responsibility to fix any broken PS4,
Pretty much any electronic device has a limited warranty.
Chance of wear and tear caused by irresponsible use increases over time, so if all companies gave out unlimited warranties, they'd lose a lot of money, and often not fairly.
Like the situation you described with running the console with little space for ventilation. Add in hot temperatures in the room, and leaving the console on for excessive amounts of time... The more months that pass, the higher the chance that something inside will break because you were irresponsible. Why should they fix that?
The thing with the controller may not be your fault, but if they make exceptions for those situations, people will expect them to make exceptions for situations where it was their own dumb decisions that broke the system, but Sony can't prove that it was.
It would be great if we always got unlimited warranty for our electronic devices, but that's not the case.
Luckily my iPhone recently died randomly within my 1 year warranty. Got a brand new one sent back to me within 2 days.
Also on a personal note, I never had any issues with my PS3 or PS4.
PS2 however got the infamous Disc Read Error after 4-5 years. Bought myself a PS2 Slim then.