Can't see why it's so hard to politely tell them you're not interested, close the door and then get on with your life without the rage some people seem to develop.
I'm not sure what the point of this post is? Are you bragging that this **** dosen't annoy you? Are you genuinley confused as to why this annoys people? Are you saying that you think that people find it "hard" to be polite and close the door? I'll give you the benefit of the doubt and assume you are serious in your question.
I'll attempt to explain it in laymans terms. I am capable of locating and purchasing everything I need. I already give a significant chunk of my salary to charity. I do not wish to assist with anyones consumer survey (I don't care how "useful" it is). Therefore, you are starting from the position that you cannot possibly be about to improve my life in any way, the BEST outcome I can see from you knocking on my door is that you don't somehow detract from my life (Like annoying or boring me).
Couple with this that I spend very little of my time sat staring at the wall. When you knocked, I was doing something, and you have interupted it. At the very least, you have interupted the flow of whatever housework I was doing. Maybe flow is not important to you when you are doing the housework, but for me, its very annoying. More importantly, I spend a small ratio of my time doing housework, so more likley, you have interupted the game I was playing, the movie I was watching or the food I was eating. Ask my missus, this is not a sensible thing for even someone I care about to do - Mr Door to door is now playing with fire.
So lets quickly recap. You have interupted me, probably in such as way as I will be irritated about it, and for a reason that can only benefit you, not me. At this stage, I have opened the door and realised what you are. I am not happy, and this is your fault. Now, I am perfectly capable of politley saying no and shutting the door, in much the same way that I am perfectly capable of cleaning dog crap off my shoe by licking it, but this is not going to really improve the situation you have placed me in, so why should I?
Now, you may not be aware, but when a person is angry, you can aleviate those feelings of anger by expressing them at the person that has caused them. This can take many forms, from telling them that you are angry, to kicking them in the face. Obviously there is an appropriate level to choose, and a man who unwisley knocked on my door to sell me sky tv dosen't deserve a pickaxe up the nose (probably), as he is not there for the specific purpose of annoying me. However, he has obviously accepted this as a side effect of his primary purpose, and as such, appropriate response range from the afforementioned 'No thank you' *Shut door* through to having obsenitys shouted at him until he leaves. I prefer to choose a middle ground.
Hopefully this clears it up for you, but if you are still confused as to whether it is a compulsion (Instead of a choise) to be unpleasant to door to door guys, or do not understand the basic human emotional responses that cause it, please feel free to ask follow up questions.