DanishbluntDegradation can happen everywhere on the phone. The manufacturer could simply say it's wear and tear and this doesn't usually get covered but even if it is covered under warranty, you still have within 1 year of warranty to repair it.
No, because its a degradation process. Much like when you use a power supply in a PC, if you use 60% capacity for 5 years nothing will happen, if you use 100% after 6 months it will die.
As for warranty, if there is a manufacturers defect, then even after official warranty you should replace it for free, there are certain laws that state this, this is also why you see extended warranty programs on apple products, it's not because apple wants to, its because they have to otherwise they will face lawsuits and will have to pay a huge fine.
Same goes for Asus, better pay a a couple of bucks for some IC replacements rather than pay millions for a fine.