Being out of shape regarding cardio is a risk factor to heart health. It's the number one killer of man. There are a lot of factors that determine a heart failure. Genetics, inflamation, triglerides, HDL to LDL ratios; total cholesterol, blood sugar, diet, body fat levels, and cardio fitness to name some.
The argument that I know a 20 year smoker that is healthy or a 15 year steroid user that is healthy is pure stupidity. They are a risk to health. You can't go to the extremes of statistics to prove a non existent point. Sure as the sun rises a good runner will die from a heart attack. As sure as that the majority of runners will prevent a heart attack from their running program.
Cardio endurance is important. If you don't believe it go down to your local boxing gym and fight a three rounder. I bet the next day you be lacing up up your running shoes.