I suppose the answer to your question is that anything designated by law as a "life-prolonging procedure" would be denied to anyone who specified in writing that they didn't want their life to be prolonged. For example, I was talking to my mother-in-law (a nice elderly lady) yesterday about the Terri Schiavo case, and she says she wouldn't want to be kept alive by means of dialysis. I don't understand that, but apparently she heard about a bad experience with someone who was on dialysis. The lady kept telling them she didn't want dialysis, and they kept doing it to her. Finally her daughter heard her say it, and made the hospital staff stop the dialysis. The lady died two days later.
I think I see your point. You disagree with the Florida law. So by your example, since air conditioning should not be considered as a "life-prolonging procedure," neither should the feeding tube. Is that what you're saying?
A desire to exclude a certain class of procedures should not be interpreted so as to exclude procedures which, when the desire was stated, existed and would not have been considered to be in that class.
When Terri supposedly made her statements, they could not have been construed at the time so as to forbid the use of gastrostomic feeding and hydration. There is no reason to believe they were ever intended to forbid such things. Reconstrual after the fact is craven.