All watch bands will be interchangeable, but there are three types (maybe 4) of bands. 1) Bands with brushed aluminum metal accents, 2) bands with polished stainless steel accents, 3) bands with gold accents and maybe 4) bands with no metal accents.
Look at the website and compare the black and white sport bands shown with each watch. The metal button is different for each model. Note also, there are no colored bands with the gold or stainless buttons. There are also no leather bands with brushed aluminum clasps/buckles. In this way, bands are limited to certain models of watch even though they'll be sold separately.
Unless you're fine wearing an aluminum watch with a stainless steel buckle, or a steel watch with a red leather band and a gold buckle etc. Personally I think it's tacky, but to each their own.
But they won't outright restrict sales of bands, and they'll certainly be interchangeable. Just not the modern leather band with the 42mm watch (I hope I'm wrong about that, but I'm quite certain that's the case).