And Murry was only 55 when he died (and Dennis 39 and Carl 51...damn...) of heart problems. I wonder if Brian takes Lipitor?
Probably this is not the most fitting topic, but -
I'd say that Dennis and Carl passed away for different reasons. Dennis' lifestyle somehow caught up with him; when you're alcoholic through and through, your heart can stand very little. Cold water could have stopped it, or perhaps he had a sudden epileptic fit (often seen in alkies). Carl had a brain tumour, unrelated to his heart. Murry himself drank a lot, ate lots of not-so-healthy food, and didn't do sports.
Brian cleaned up when 40 - that is a relatively young age and the body can recover still from overeating and chain-smoking and all the other abuse that Brian was cursed with.