I have a friend that tests the welds on the track of Space Mountain every year. They don't close down the ride because they do checks like those when the park is closed. I'm guessing it closes every year because of how old the attraction is. But I don't think every attraction closes for refurbs every year. Although they do have annual checks to make sure everything is working properly. But those are done during graveyard with contractors. In park maitenance can only do so much.
Every ride is supposed to go down annually for a refurb, some longer than others. When they put them off, the rides have to be down longer. That's why we see Indy going down for 3 months at a time rather than the 1 it should get annually.
And why WDW's attractions look the way so many of them do. They only get minimal work for maybe a week every few years...
So yes, the yearly Matterhorn refurb may be annoying, but it's not too bad in the big picture - especially since many tend to expect it.
The water also tends to rust the track itself. This especially happens on the station area, and a lot of breakdowns are caused by the drive and brake wheels at the station going down due to water and rust issues. They're working on a way to make it so they don't need to do that sort of thing anymore.
As it stands today, the bobsleds brake by being pressed up from underneath into brake pads that replace the "below track" wheels you see on other rides.
Ever wonder why Matterhorn is so bumpy? There's nothing holding them to the track on the bottom of the rail, so over dips and hills, it physically lifts off the track and knocks the brake pads.
Take a close look at the sleds when you're alongside on and you'll see.