Ricky Gervais is, of course, a particular kind of sour sad sack, but one that has a great deal in common with funny Puritans as well as the British tradition of assuming that things are inevitably going to go somewhat badly. Brand is, and I'm sure this is why he was cast in The Tempest, a particularly potent manifestation of British anarchic humor, a holy fool. He easily could have starred in The Young Ones, or taken Michael Keaton's part as Dogberry in Much Ado About Nothing. We have clowns in America, but we mostly laugh at them. Steve Carrell, for example, often plays idiots who are simply and totally that. It doesn't make Brick Tamland less funny that he's just transcendently dumb, but his idiocy doesn't lead us to any deeper truths. Peter Griffin's not a holy fool, he's just an idiot, and not always an amusing one.
Brand, on the other hand, often seems to operate on the principal that if you go truly batty, truth lies on the other side of silliness or madness or extreme carelessness, and sometimes can be reached only by those means. It's the same principal that underlies some British humor: it's only when you push too far into the realm of absurdity or disgust that you can find and understand certain things. Jackass may be the sole American exception, and even then, there's more laughing at than with.