Yes, it will change as they work through the application. Everyone needs a medical, no matter where they're from; they just don't want you to go do it until they instruct you to.
My account has identical statuses to all of yours (except biometrics are completed). It's a bit of a mystery why some of ours say the background check is already in progress this early on and some don't. I have some foggy theories that maybe it has something to do with the PA/whether they're from a visa-exempt country, but it's all just a guess. At the end of the day I wouldn't put too much stock in it (alas!) -- I expect our applications will take just as long as everyone else's, but our statuses will just stay the same the whole time. That said, I have noticed that applicants from the US are generally processed quite a bit faster than the rest of us, so you probably will advance more quickly either way.
Whoops, sorry @CanAmAus, I just realized after reading @missblueyez's post that my account has a different status than yours next to "Review of additional documents" -- mine also says "We do not need additional documents." (There's been so much discussion of the background check line around here, I just skimmed right over that other line!)
