You know, I have some experience with this. I had a friend in college that had parents that never once argued in front of him. Not once. This guy was completely unable to resolve any conflicts. You know what? People learn conflict resolution by watching others, and that goes for kids.
To give more details about my friend, he was a really nice guy, but he avoided confrontation like the plague. The problem is, you can only avoid it for so long. When he finally did get into it with anyone, he would literally start to fall apart. It drove him to drink and eventually most of his relationships fell apart and he became a binge drinker/alcoholic. He ended up dropping out of school and disappeared from the face of the earth. He drunk dialed me years later and left a message on my answering machine (without any details about where he was). A very, very sad situation.
I'm not saying everyone will react like this, but that watching an argument be properly resolved is a good thing for a kid to see.