Really? Or are you being sarcastic? For the most part the HN crowd thinks like Kay from Men in Black: "No, ma'am. We at the FBI do not have a sense of humor we're aware of."

Slashdot has always highly valued humor. "+5 Funny" is a highly sought after moderation. So, perhaps in reaction, HN usually downvotes attempts at humor.

Neither approach is "better". It's just how the respective communities have evolved.