Wouldn't the ability to not mix-and-match make it easier to mass produce them?
No. Because they can make a crap-ton of the silver aluminium and just run different dyes of bands. If the silver bodies were a higher priority for Apple to manufacture the SG ones would get delayed.
That said, it's also possible the SG is this year's white iPhone. But, the fact that some people are getting SG watches on launch day make me hopeful I'll see something shake loose next week.