Hmmm...but 1 stab wound might not be enough to stop some people, especially if they've got the adrenaline pumping from committing a crime.
This has always been a dodgy area of the law I assumed (self-defence killings) and really we can't judge. If it is as clear cut as it seems though, then I hope the bloke who did the stabbing gets off scott free - I would do exactly the same in that situation.