Well, that's the idea anyway. I build a beginning of a prototype of the "degrading world view" in a software simulation game once - years ago, but the idea stuck.
What happens when you run into something unexpected? The cat decided to nap on the rug in front of the fireplace instead of in the window? In order to not vacuum up the cat (or whatever it is your robot is doing while wandering around), you still need to determine that there is, or is not, something in the path. If not, go that way. If so, you need to add that object to the map.
While the "degrading world view" sounds interesting, and is a good way to deal with cats, assuming that walls won't be there after a period of time isn't realistic.
People don't operate under that assumption. They assume that walls and other "permanent" fixtures will be there tomorrow, next week, and next month.
Of course, people also rebuild the map constantly, because we see that the wall is still there, the couch is in the same place it was this morning, etc.
Too many people think that they can program a robot to run around building a map, and that once the map is built, nothing ever changes and the robot always knows exactly where it is on the map. I'm glad to see that you realize that neither assumption is true.