"You would naturally expect the value of a home to decrease by some amount each year."
If you deduct maintenance from your home value, it more-or-less does. I don't see why a maintained home "should" decrease in value, though. A lot of the value of a home is in the structure, which tends to wear much more gracefully than, say, a car's body.
There is little that maintenance can do to prevent a 100 year old foundation from 'settling' in a pretty precarious way. Or finding out one day that the water pipe is a 100 year old wooden pipe that is now rotted through. As a house gets older, maintenance ($) turns into renovation ($$) then critical overhaul ($$$), even in the houses with good bones.
If you deduct maintenance from your home value, it more-or-less does. I don't see why a maintained home "should" decrease in value, though. A lot of the value of a home is in the structure, which tends to wear much more gracefully than, say, a car's body.