There are no hardware differences.As the report notes, users attempting to use a Verizon iPhone 5 on AT&T in the United States will not have access to AT&T's LTE network, due to hardware differences that leave the Verizon iPhone 5 (which is essentially a single CDMA/GSM world-mode phone for 3G purposes) incompatible with LTE frequency bands 4 and 17 used by AT&T and Canadian carriers.
https://www.macrumors.com/2012/09/21/verizon-iphone-5-confirmed-to-be-unlocked-on-gsm-3g-networks/
The phones all use the same Qualcomm chip.
It's programming in the base band radio that determine what frequencies are enabled.