I think the most plausible reason to do this would be to avoid future confusion if they decide to introduce new band sizes. Also, the current differences in ca

I think the most plausible reason to do this would be to avoid future confusion if they decide to introduce new band sizes. Also, the current differences in case sizes mean that band sizes are slightly different when used with different watch models, even if the band width is the same. The same solo loop on a 38mm watch fits slightly smaller than the same exact band on a 40mm watch, even if they're the same mounting mechanism. So, to be precise about fit, you already need to specify the watch size specifically, even if the band width is the same.