My sister and I have decision making power for my elderly father who sounds at the same place healthwise as KrissK's aunt. We discussed this exact scenario just last week and decided that while, we'd consider medical input, we'd probably chose comfort care. We also rejected knee replacement surgery and cataract surgery for our 85 yo mother.
Now, none of the costs would have come out of our pocket - what with UHC and all. However, we don't all require a financial hammer to do what we believe is the right thing for our parents.
Of course, I slaughter my own pigs and chickens so perhaps that's what did it.
It helps immensely that they both have living wills - Dad's is especially clear starting with "anyone who knows me will realize". A living will is a huge gift to family. And to draw in discussion from another thread, our medical providers and family should be aware of our feelings about end of life care issues.