Folk is lacking in songs done in minor keys. But then, there might be a good reason for that. I have always found stuff done in a minor key to be 'depressing'. It is certainly difficult--though not impossible I think--to write a humourous song in a minor key. I think it would have to be very dry humour, for sure. As to jazz having more minor stuff, yeah, probably. The one think I find funny is your friends either/or thing. I like jazz because it has more . . . . When I'm hungry for spaghetti, only spaghetti will do. When I'm hungry, it doesn't have to be spaghetti.