5 Minutes can be pretty long when you don't train cardio. Ask Shane Carwin, who is a professional athlete and even trains cardio. To neglect cardio in training for street fighting is plain stupid. Yes, often a fight is over in a few minutes, but you never know. You don't want to gas in 30 seconds. And in case you have to run away, you want to have a gas tank to be able to do so.
That's putting it lightly. I consider myself a fairly well conditioned athlete, but if I don't pace myself I can definitely gas within 5 minutes. And thats the thing about real fights -- the adrenaline dump! You burn through energy like a torch through newspaper. The average guy will have like 30 seconds of fury -- give or take -- after which his intensity will start to fade. For all of the training I do, I think I could only go 100 percent balls to the wall for 2-3 minutes before fading, but that's still a huge advantage.
And having the cardio to run away is SUUUCH a good point. I didn't even think of that, but that's so true. I find it so ironic that the same self defense enthusiasts (thats what i'm calling them, since the vast majority haven't even been in real situations) will say things like "its about survival on the mean streets. I'll eye gouge him then run away!" will also say "cardio doesn't matter. there aren't rounds on the streets" in the same breath.
Id rep, but apparently I need to spread some more around first.