It's a bad example in the article, I think. Substituting challenge for problem may have shifted the sentiment of a sentence from negativity to possibility in the past, but that particular example has been used so much that when I hear people talking of their challenges I immediately have a feeling that not only is there a problem - but that the speaker is evading that fact.
ofcourse, good point. but there is a difference in the way a sincere man says 'challenge' and the way that a phony says it.