I don't know for sure, but I think there is some difference in the elasticity. Remember that nominal width is just the unstretched measurement. Plus, the length is also somewhat important (not for comfort but for effectiveness).
It certainly can't all be "in our heads" - I am very uncomfortable if I use a regular condom. I was fed up with it, so I used an online retailer to put together a trial package of lots of different brands, using the website's size chart as a guide.
It worked: Now all I use are Kimono Maxx Large Flared condoms. They are a very "light" thin latex, which seems to make them very stretchy. They are 2.09" (53 mm) unstretched on the shaft, but 2.6" (66 mm) unstretched on the head. 7.9" (200 mm) long.