When has one person or one team, in the history of sports, deliberately lost so that some higher ideal could be reached by the opposing person/team? That happens each and every practice in the martial arts. One person takes the "losing" side of practice, but in reality, it's never a "losing" side...
Ever hear or see a really good British Soccer player in a game, coming down to score a goal -- know that he can score because he is that good -- but decide to dial down his skill level so that the opposing team's goalie can learn to block better...
Yet that very same mindset happens in good martial arts all the time.
I don't completely disagree with you, but you're comparing apples and oranges here. Keiko is training, and a sports match is competition. Training vs competition has different purposes.
If you look at sports training, rather than competition, you will see similar behavior to Keiko. Athletes will tone down their plays so that the other person/team can practice and get better, and depending on how the specific sport works (like with something like wrestling for example), you will also see individuals purposely take the "losing" side so the other person can practice/experience "winning".
And if you're talking about the "spirituality" of sports, the exact sport in question is a factor. Some sports are much more "team based" then others. Take Football, for example---you have the quarterback and the receivers who get all the glory, but their success is largely dependent on the actions of the linebackers or whoever. Those guys don't exist for their own glory, their role is totally to support the needs of the team. Or take a Nascar racer's mechanics, it's easy to forget that they even exist.
Those types of "team" sports are certainly a minority, but for this type of discussion, I think it's problematic to lump all sports together.