Insightful and very true. I would also extend the relationship to really good DPS, who help the tank do their job rather than make it harder and give their all in CC to protect the healer. Felguard Stuns Save Lives. Although I'm not allowed to tell any of Honey's little friends I make him save people. Even a warlock has to draw the line somewhere.
The relationship is definitely strongest for a regularly paired, raiding tank + healer. These so routinely codepend that a strong bond is necessary, if just to prevent either freaking out under stress!
WRT the protector/nurturer gender roles. I find women (in general) have a strong preference for druids, then mages and priests. No warriors and or paladins to speak of (one of the droods I know does have an unloved 70 protadin). However the role split is equal, all the female droods I've known tank or want to.
At the same time I see plenty of men (including myself) enjoying healer roles in a protective way. When I heal instead of thinking "I'll sustain you, make you strong so you can protect me" it tends to be "I won't let you die!". Almost as if we're in opposition, though I really do appreciate a good tank! Maybe I'm just nuts, I also enjoy it when the tank loses control and I get to flex my +heal a bit ^^;
This may partly be because I tend to gear hard, so I'm usually numerically stronger than the tank. When I'm not, it's usually because we both massively outgear the encounter. It could also be because I almost exclusively play with paladin tanks outside raid. If DPS behave panic-tanking situations rarely arise. It all boils down to the tank depending on me going above-and-beyond way more than I depend on zir.
It seems to me that both genders like both roles, but perhaps perceive them in a different light?
This is an interesting discussion for me partly for the possible crossover to motivating women to choose scientific careers, specifically computer science. At the moment most women do not seem to perceive a career in computer science as rewarding, while they happily take up careers with close parallels like law. Admittedly law is very prestigious, but women are no more likely than men to seek high prestige jobs. If we want more diversity in code labs, we need to understand the difference and work to address it.