My 2015 OB 3.6R with 38,000 km has the same rust in the same area, so does my 2004 Mercedes with 127,000 km.
I've attached 3 pic of mine, again at 38,000 km, I live in Canada on Vancouver Island (west coast of BC) not much snow in my area. So, don't sweat it, be happy that you bought a Subie!
In Michigan, that's perfectly normal for ANY car, whether it's garaged or not.
Just as a suggestion, a tip I learned from my Dad a long time ago was to make sure I carried an uncoated wire clothes hanger with me, as well as a pair of pliers. That way when your exhaust pipe, which WILL rust through, falls down and you're in the middle of nowhere, you can use the wire and pliers to rig up a little loop to hold it up off the ground so you can drive into town to a muffler shop. And yes, I have had to do that.
I'm sure you've seen the pickup driving down the road where you see through the holes in the side of the bed that have had rust eat through - and some of those aren't old beaters. The way these cars are made is with electro-deposition of the paint, including the first coat, which is actually put on while the car is completely submerged in the base coat paint. The actual spray colors and top-coat are also put on via ED as well. Net result is that unless you scrape it down to the bare metal, the car CAN'T rust through.
Now, what does sometimes happen is that when some bolts are manually put in through the weld nuts (which are put on in body shop and also painted), they can end up scraping some of the paint off and get it down that far and then cause some surface rust. But the air tools are normally designed to not over tighten and click off before that point.
This is process is similar to electro-plating and does the same thing as hot-dip zinc galvanizing, it's just that you can then paint the finished product, instead of just having that shiny zinc coated surface.
If you are concerned over surface rust on the exhaust system, you can lightly sand and paint it with BBQ grill paint. I did this with a Jeep Wrangler once.
Chips from road abrasions + salt + slush = rust on panels unless aluminum. My 10 yo truck has zero rust on panels or frame because I don’t allow it. Key is winter washes with spray wax. Chips touched up. If you pass travel all winter any vehicle will be eaten unless aluminum which will Dent and chip but not rust.
Weekly coin wash, I have a coin jar that I put all the change in and once a week I go and power wash the car thoroughly, my dad did that with his 89 Accord, that thing was pristine even when he traded it in in 2003.
Very interesting to know! Glad to see Subaru taking rust prevention seriously and yes every 5 year old pick up in my works parking lot is already rotting around the bottom of the doors, every single one of them
Drain plugs, it was a huge issue on BMW's too with ones made in the 90's/early 2000's, often the drain plugs get stuck with gonk/leaves etc, then the water just sits there and rusts from the welded seams.
I was surprised to see similar rust on the suspension parts on our car when it had 12km on it. The plan is to get it rustproofed anyways but its not exactly confidence inspiring.