Well, when the gladiatorial custom first began, it was mostly a ceremonial practice to commemorate important events or people, in which someone was expected to die as a sacrifice. As the gladiatorial custom evolved into a spectator sport, although people still wanted to see death in the Arena, the people who put the shows on were more pragmatic about it.
The record shows that later, some matches were advertised to the public as being special because one of the fighters would actually die. However there were really several varieties of gladiatorial matches. Ones were criminals condemned to death were pitted against each other, ones were career gladiators fought each other which were fairly uncommon, ones that were put on purely for the sake of showmanship such as recreating a Roman military victory, and so on.
Later, under Emperor Augustus, (Roughly 50 years after the Spartacus revolt), Gladiatorial matches where someone was certain to die were banned. When later Emperors overturned this by having popular gladiators who were defeated in the Arena killed, their popularity was severely impacted (see Caligula).
What I mean by faked is not that the shows did not have real violence in them, they certainly did, but in some occasions there were Gladiators who "died" in one match in one city who were then shuffled around to other cities to put on shows there, only to return for a rematch some time later. The faking was not in the potentially serious injury some of the men faced, but in the claim that some of them died when they didn't.
According to wikipedia a Roman source claimed that the death rate among all those who entered the Arena was about 19 out of every 100 between 1-100 AD. Not too bad considering what the job is, and it's not clear if this includes only professional gladiators rather a mixing both gladiators with the truly condemned.
Also, there was another sort of faking in some games. The Emperor Commodus famously fought in the Arena (see the movie Gladiator), but his opponents invariably fought with wooden training weapons. He was not killed in the Arena.