That's cos campag 8 speed, campag 7 spd and shimano 7 spd are all 5mm nominal spacing. So, if ever you struggle to find another campag 8 speed wheel, you can pop a shimano 7 spd wheel in and it'll work (less one gear of course). The hard bit will be finding another campag 8 rear mech if that goes, but there are options, but that's another topic