"I have also realized that those who find it so easy to say I will die for you are the very ones who chicken out when the time comes to put actions into words."
I think that's probably it, people who say this like it's a no-brainer (not always, but in general) are probably compensating for something.
The problem with questions like this is that they aren't realistic. It isn't a part of our reality that you ever get the choice of who gets to live. (There are times where you need to defend somebody. But even the extreme-- and totally rare-- case of diving in front of a bullet for someone, it's still not a guarantee that you're going to die from it. Nor does it seem like you're guaranteed to be safe if you don't. There's never a clean decision of which one of you lives and which one dies.)
It's like ".....you can only do one thing, jump into the lake and save the drowning baby, or open the treasure chest with $10million in it, which would you choose!?!?"
It isn't a situation we were ever faced with as we evolved to this point, and it isn't realistic that it would ever come up.
I do think some people probably genuinely mean it when they say they would die for someone else. I just don't think it's a useful thing to be concerned with (and agree that it's silly for that person to have rifted their relationship because of it).