Having played Necromunda, WYSWYG is huge in the culture. Being that SW:A is a necromunda spin off it makes sense to follow the culture requirement. That said, a Necron player can literally make a team with 1 box of immortals. Sure some races may require more to get the right weapons, but that's the key here. The focus is such a small model commitment, players can easily get bits (ebay), magnets, or additional models. The main requirement is because this is expected of all necromunda players previously.
That said, many wargear items don't require WYSWYG outside of primary weapons (ammo reloads, etc). A lot of wargear falls under the 'stored in their pockets, etc'. Oh and i'm a HUGE fan of hostlered pistols, that was a nice thing last time I played necromunda.