Wallbot

Due to a recent moth infestation that we've been vigorously fighting, the walls in my house have little stains on them. This is, needless to say, annoying.
I'll probably wipe it up with cleaning sprays and towels, but I'm not the only one to have this problem. I understand that parents often have children who either inadvertently throw food at the wall, or doodle on it with crayons. So, how can I clean the walls more...automatically?
I suppose the best way I can think of is to take the "Roomba" approach and have a robot. The robot would wheel itself alone the walls, sliding up and down on metal supports, scrubbing grime from the walls, sucking the soap and absorbed dirt into a special container, and periodically leaving the walls to go dump its bin into a nearby sink.
I think people will really like this. iRobot's robotic vacuuming machine, the aformentioned Roomba, is so popular that people treat it not as an appliance, but as a pet. People will actually sweep their floors for their robot so it doesn't have to "work" as hard. Which, mind you, it is a robot. It at worst does not care, and at best could be said to actively enjoy cleaning.
You could write entire psychology books on that topic.