Cleanliness what is the definition?

I know that I said I was taking a posting break, but I had to blog about this. I don't want to offend anyone who reads this so know that my definition of cleanliness is just that my definition. Also know that I think there is a very large difference between houses cleanliness and a house being picked up.

So any of you who read my blog know that we are moving next week to a house that needs a little work, so Luke took a few days off of work this week, my Mom took the kids and our plan was to work, work, work, and we did just that. Thursday my new appliances were being delivered so I worked very hard Wednesday, and Thursday morning to get the laundry room ready. After scrubbing every wall and wiping every surface, I moved on to painting all of the walls. Next I shined up the cabinets with pledge, and mopped the floor for a second time. Ahh yes the laundry room in my definition was clean, but for some reason it smelled just awful. So after running through everything that I had done in my head it hit me I never vacuumed out the heating vent, but this smell couldn't be coming from the heating vent, or could it? So I went out to the garage grabbed the shop vac. a was going to clean it out, but I decided I didn't want to because it might be really gross so I asked Luke to do it for me. He pulled off the heating vent and I head, "you have got to be kidding me, what's wrong with people." Curious I walked into the laundry room and asked what he had found, his response was not something that I can post, but we had identified the smell. Yes the people who had lived in our house before us had been using the heating vent as a place to put what they had scoped out of their cats litter box! At this point I left the room feeling very sick to my stomach, but this is what crosses my mind:
1-I'm so glad that Luke is cleaning that and I'm not.
2-It's a really good thing that the gas has been, and still is turned off and the heat hasn't been on.
3-I can't believe that anyone in their right mind would do something like that.
4-I'm so glad that Luke is cleaning up that mess.
5-I love my husband, he's not complaining about the mess as much as I would.

So the mess has been taken care of, and every vent in the house has been cleaned. My laundry room smells just fine, and I still am very excited to move in to the new house. After this experience though, it got me thinking, I had been told that the house was clean. I have been working on getting the house to my standards of clean for almost a week now, and I still have work to do. So what makes people decide to live in filth? Is it lack of motivation in life, or that the standards were never set, and as an adult they don't really know what clean is? I'm interested to hear what others have to say on this subject. Were do you think each individual persons standards of cleanliness come from?