Ah! Another 'Show Boat' fan

(although I must admit it's Helen Morgan who knocks me out in THAT film

).
I think there's a prejudice against comedians when people consider acting. I remember watching Laurel and Hardy's 'Our Relations' and being struck by a scene in which Hardy has to render various stages of 'dumb' in response to whatever's going on. When it's well done, this kind of thing just flows by and you accept it, until you think about how hard it must be to do. Did you ever once watch a W.C. Fields movie and have the word 'actor' enter into your head? Never, right? The guy's so good that it's subconsciously inconcievable that he could have been anything other than that character OFF screen, so it's hardly acting at all... or is it?
Chaplin, on the other hand, had a different (and unique?) style. To me, you never think: 'Charlie must really be The Tramp', but 'Charlie must really be that guy who I see CONSTANTLY winking at me from behind The Tramp.' To me, Chaplin is ALWAYS 'on.' Always the showman. Always fully aware of his brilliant comedic abilities and his ability to manipulate the emotions of his audience. Like Al Jolson, I don't think he's up there to act. I think he's up there to entertain. Perhaps this helps us understand why the Academy ignored him.
Maybe I haven't seen the right Garbo films, but I don't think of her as a great actress, either. Certainly, until I saw some of her silents, I didn't even understand what the fuss was about. She had mystique, surely, but her acting leaves me cold (and it's not her accent, either, since I think Ingrid Bergman was a great actress and she certainly had an accent to deal with as well). As for Hitchcock... well, you got me there, because if Hitchcock wasn't a great director, no one was.