Hardware differences between iPad, iPhone, iPod models within a single family
While I can't find you documentation describing the exact hardware differences of each carrier's iPhones and iPads, it is to my knowledge that all Apple devices are relatively the same across the board, save cellular hardware.

However, Apple is known to source different components from different manufacturers, but there is nothing I can find to determine whether or not a certain carrier set of iDevices uses different hardware universally compared to another carrier.

An example of this was Apple's controversial sourcing of LG and Samsung displays for the first MacBook Pros with Retina Displays: https://www.youtube.com/watch?v=KdhIA8-UIRQ

Wrapping it up, Apple may use components from different suppliers that may be marginally different in some aspect, but there's no evidence to suggest that one carrier has a different hardware set compared to another, excluding cellular hardware.

And with Apple's philosophy of delivering a consistent and delightful user experience no matter what type of Apple device their using leads me to believe that the differences in those components are negligible (though there was anger regarding the aforementioned rMBP display snafu).