What makes a good comedian a good comedian?

I have just recently been to watch the most awsome Billy Connolly and found my self virtually passed out as I couldn’t breathe I was laughing so much, it wasn’t so much always what he was saying (as sometimes you knew what was coming) but they way he said the joke!
I was wondering what makes you laugh when you are watching a comedian? Is it timing? joke they told? the way they tell it or all 3??

http://www.youtube.com/watch?v=SzZzGxReXmo
http://www.youtube.com/watch?v=PyW0riD54nY&feature=related
a couple of examples above for those who haven’t heard of him