I don't think the root checker is there to "necessarily" deny warranties. Only reason I say that is the minority of Android or iOS users root or jailbreak. The majority are just fine with whatever device they are using and the firmware they are running. And most people using Android that want to change the look of their screens, app drawer, etc can just use a third party launcher without needing root access . I believe with the share everything plans offering free tethering, the root checker is there to see who is grandfathered into unlimited data and is rooted to obtain free tethering, unless you're using foxfi 
