If you take care of your stuff, you wouldn't need a warranty to begin with. And while I do understand that accidents happen, and some people are just clumsy, a "regular consumer" would probably not give a stuff if the phone runs faster than another or not. If you are a regular person who needs a phone, you will get a phone that you think looks good and completely disregard how much RAM the OS uses.
EDIT: Forgot to mention, I have a S5 and it's perfectly functional with TouchWiz. I've had no problems since day 1.
a warranty is always needed and a nice bonus. any phone is prone to just pooping with you doing nothing to it. coming out of the box dead or broken or pixels dying.
anyway a regular consumer does care how fast their phone is. nobody wants something that is disgustingly slow or not capable of completely simple tasks fast. its all about speed. i dont think anyone would enjoy an android or ios that runs at 2 frames per year.
also i doubt ram has that much to do with the speed of the device. i had 1 gb of my note and 700mb was usable and always available (any os i used including cyanogen, 300mb was always used by the os, no idea why) because i kept it clean. still was frustratingly slow at doing things.
maybe i had a bad run with samsung, but 4 devices in a row (i was a samsung fanboy, constantly stuffting on every other company too), yeah i dont know.
fortunately for me i now own an iphone so i dont have to deal with them again
edit: yeah the S5 is pretty nice. S5 is the only one that i dont have a problem with. but op doesnt have that choice. its S4 and nexus 5. the nexus 5 is better.