Sorrels et al. (2007) carried out their work in the San Francisco Bay Area of California. They studied 163 male subjects which included both circumcised and men with intact foreskins. Nineteen locations on the penis were tested with the Semmes-Weinstein monofilament touch-test. The glans of the intact males was found to have greater sensation than the glans of the non-intact males. The area of greatest sensation on the non-intact males was the circumcision scar. Intact males had five areas located on the foreskin of significantly greater sensation than the circumcision scar on the foreskin. The preputial mucosa, the mucocutaneous boundary and the ridged band were found to be areas of great sensation on the intact penis. Taylor has postulated that the ridged band is sensitive to movement (Taylor 2000).

Logic-wise, the more you're expose to something (whatever it is), resistance / immunity / decrease of feeling/sensation will occur. Personal opinion though.