Most of those mentioned I recognise as actors in comedic roles mostly (apart from the Brits). Do those American actors/comedians do 'stand-up' comedy? There are some 'actors' that cannot help but be funny - John Cleese for one.
When I think of comedian I think of Benny Hill, Ronnie Borbett and Ronnie Barker (fork 'andles!) Morcombe and Wise... I grew up laughing at them. Now my favourite (stand-up) comedians are...
Eddie Izzard - a professional transvestite, covered in bees and waving a bananananana
Billy Connelly - great when I can understand what he is saying.

Bill Bailey - a wizard in a call centre
Ricky Gervais - political animal
That's odd - I have just realised that all my favourite comedians are Male and British. Eeek! I do remember seeing Bill Cosby on TV years and years ago with Diana Ross and it was one of the funniest comedy sketches I have seen. But not as good and the two Ronnies and their four candles, 'o's....