I will make an alternative theory: 'K' sounds can be funny, but are often used to connote a strong presence: Kojak, Kolchak, Kowalski (Vanishing Point), etc separate from comedy.
'Z' sounds can make a word funny, perhaps because of the pleasing buzz of the tongue (and see- wasn't it fun to hear the word 'buzz' in your head just now):
Hans and Franz
Xylophone (even funnier because it doesn't have a 'Z' in it)
Zeppelin (used best in breast references)
Fuzzy Wuzzy (vagina reference)
Gonzo (works for Muppets)
Okay: forget that last one.
I am The Replacement Laslo.