Murder mysteries are among the most conservative of literary genres. Though their plots revel in crime, corruption, lies and death, the understanding is that murder happens for a reason, and those reasons are discoverable, even if the perpetrators are not always apprehend able. There are many brilliant exceptions to this formula — most sophisticated mystery fans will already be silently mouthing them — but that is the formula at its simplest.
Comic writing, especially the black-hearted kind, is possessed of a much more anarchic vision, one that delights in disorder and sees no reason to correct it. When a murder occurs in a comedy, the reason behind it is often irrelevant or non-existent. Simply put: Nobody really cares why or how Bernie died, they just want to watch two goofs spend a weekend with the corpse.