Like firefrog, I don't have anything against Munch belching, though I can see why you would say it's unoriginal.
As Firefrog said It really just something that allows you to customise the way you play... sort of like developing your own view of Abe/Munch's character. For example, I sometimes make abe and munch continuously make the sounds as if they are having a competition, making them seem like little kids.
The burp in itself is not that funny, but burp at abe and he'll say something like "dude that's just wrong". I don't know why but I find that funny. Same goes when Abe farts at Munch.
