i have to admit i don't see lag on my s4. i also have to admit that i start disabling and turning off stuff i don't need/use immediately after i set up the phone for the first time.
i don't use touchwiz launcher. nova launcher prime is my launcher of choice. i've disabled all of the bells and whistles i don't use under settings > my device > input and control. i have not adjusted any graphics or animation settings. there might also be other apps or syncing services running by default that cause lag, but again, i disable all the stuff i don't use so probably another reason i don't see it. my s4 is smooth as can be and hasn't had so much as a burp.
i agree a high end device like this should be lag free out of the box, and for some it might be. but i know better. android is made to be tinkered with and modified. it doesn't help that pretty much every option possible is enabled out of the box and sometimes causes stutter because too much is going on. that said, i think people's perception of 'lag' is skewed due to the buttery ui of apple products. but there's distinct difference in functionality between the two platforms that most people don't see. both are good in their own way, but android gets a bad wrap when compared to apple's eye candy.