In fact it is fair. People can and should be possible to kill more easily during their sleep. What is not fair is that towns are supposedly safe places. Why exactly should it be impossible to slay somebody in a straight-forward manner in a town when you can do it just fine outside of the arbitrary border separating a town from the wilderness? Rather than the sleep duel being an ugly bug, I'd say making the towns safe from direct PvP is a compromise the designer had to make to draw people in in the first place. Whatever method was used to kill the two poor saps in the latest ep was another crack in the unreasonable safety of the towns, and I'd bet the designer left such gaps there fully on purpose.