Should A Professional Athlete Ever Quit?

"At what point in a Grand Slam final does a player decide to tough it out though illness or injury, allowing an opponent to win the traditional way — closing out the contest on match point?
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Or when does that ailing player decide that a loss seems likely, the pain is unbearable and continuing is simply not worthwhile?
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The Australian Open women’s final, won by Amelie Mauresmo on Saturday when Justine Henin-Hardenne retired with stomach problems trailing 6-1, 2-0, highlighted such questions." http://msnbc.msn.com/id/11073716/
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I'm of two minds about this one. While I cant exactly comment on whether Henin-Hardenne was feeling "sick enough" or not, I gain a little bit insight when i think about the way that I feel when I am under the weather and exercising. I give up. I cant do it anymore and I stop and go home.
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But, the different is that I only have a duty to myself as to whether or not I perform.
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But how does this differ when you are a professional player? For professional sportsmen and sportswomen, training to be mentally fit is half the workload. And people pay money to see you give 100%. You are a form of entertainment and professional athletes receive a bucket load of money because of this - people are willing to pay huge money to come and see you give everything you have got - blood, sweat, tears. They train hours on end to ensure that they are physically AS WELL AS mentally fit to give everything they have got.
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Is it okay then to quit?
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Or do I have no idea what it feels like to have unbearable pain?
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In the 2004 Athens Olympics, Sally Robbins was a team member of the Australian Eight rowing team. Robbins ignited a nationwide debate and the fury of her Australia women's coxed eight crewmates when she stopped rowing late in the Athens eights final, costing the crew its medal dream. It was alleged that Robbins had a "mental blowout". However, this occured at the Olympics. The pinnacle of the team's career. Was it fair that she gave up, or was it something over which she had no control?
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Does the Henin-Hardenne situation differ from Sally Robbins?
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While not in a team situation, I think Henin-Hardenne let down Amelie Mauresmo by pulling out instead of toughing it out.
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I think Henin-Hardenne let down the people that keep her in a life she is accustomed to as a professional tennis player.
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As Amelie Mauresmo said in the press conference afterwards - "[She] was ready to die on that court today." Why wasnt Henin-Hardenne prepared to do so as well?
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Or perhaps we do expect far too much from sports stars.
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