You mean, you're concerned that the doctor would intentionally misdiagnose? What's his motivation?
The misdiagnosis can come from a personal philospophy of what kind of life is worth living, or from a triage-like consideration that others are waiting for an empty bed. It is hard to keep philosophical and economic considerations from a medical diagnosis in extremis.
Just for the record, if I were in Terri's condition, I would like to be fed and given water.