I think Karen is telling the truth. The people that contradict her (Kenny, Travis, the dancers, etc.) are on AEG's payroll. I think they're being told to say that he was healthy. BTW - apparently one of the dancers is saying on facebook that Karen is telling the truth.
The fans that saw him that week were very concerned about his health.
I liked This Is It, and parts of it were just wonderful. However, there were some parts were he was clearly out of breathe and starting to struggle. I noticed right away that he would were at least 3 different outfits in every song. I didn't realize that the songs were spliced together because he couldn't rehearse through a whole song, though.