Indeed, people need to realize that there's a difference between declining to force-feed someone who is dying and who will die in short order even if fed, and denying food and water to someone who would not otherwise die (at least not in the near future).
Also, perhaps someone can correct me if I'm wrong on this, but my understanding is that the body can only survive so long entirely on "auto-pilot" and that certain higher-level brain functions are necessary to keep things properly in balance. While it would be theoretically possible for someone to have the higher-level functions necessary to maintain balance and yet not have enough brain functionality to ever regain full conciousness, the brain is sufficiently adaptable that it would be more likely that either the damage would not be so severe as to prevent ever regaining conciousness, or else it would have been so severe as to result in death (or the need for more significant life-prolonging measures) within a matter of months. That Terri has survived for years on nothing but a feeding tube would suggest that she was less-badly damaged than Michael et al. have let on.