Sure, Angels like other cichlids get territorial when they breed. Most likely no other angel will die in the same tank when an angel pair forms. All the pair will do is try to fend off the other angels from their eggs. Sure some folks have ended up with angels dead. But to generalize that it will happen all the time is stretching it.
I've been breeding angels for over five years now and I have yet to see dead angels when a pair form in my pair off tanks, which goes anywhere from 20g to 55g. Sometimes I don't even notice there's a new pair until the eggs get to the wiggling stage.
However, when pairs form, the best course of action is to separate them from the other angels or fish either to their own separate tank or by sectioning their tank.
I've had two pairs of breeding angels lay eggs in the same tank with no problem and it was only a 10 gallon tank.
All my breeding pairs are in 10 gallon tanks with only a corner filter. I have 10 or more pairs at any given time.
I've even seen local breeders use 5 gallon tanks for their pairs.