The warranty is pretty specific.
This Warranty does not include failure caused by improper
installation, operation, cleaning or maintenance, accident, damage, misuse,
abuse, non-ASUS modifications to the product, any software programs, normal
wear and tear or any other event, act, default or omission outside ASUS’
control.
In other words even if you change/add the RAM in the so called user service panel or even change the HDD they can summarily deny warranty coverage unless the modifications were done by an authorized ASUS service center.
Would the entirety of that stand up in a court? Probably not but such things are drafted with the intention that no one will challenge it over attorney costs exceeding the cost of a new machine. Bottom line, if you change anything make sure first and foremost that you don't cause any damage doing it or tracks that you have been where you should not have. Secondly, save all original hardware in its factory state including hard drives. Replacing the HDD is the very first thing I did however the original is in its pristine state along with all of the ram sticks in the original box and put away for safe keeping. I changed out all of my sticks and you cant tell I was ever in the machine. If it needs to go back for service all original equipment will be put pack in.
How a company handles warranty issues is more about the integrity of the company than it is whats written on the warranty card. If you look deep enough pretty much every companies written warranty gives them the out to claim that failure was not their fault. What separates good customer service from the rest is how they handle it. Get a bad reputation and you wont have to worry about warranties any more as no one will buy your goods.
“Two things are infinite: the universe and human stupidity, I'm not sure about the former” ~ Albert Einstein