No, I don't know why.
In life and death selections, I don't see how you can choose to move on medical knowledge/history or emotions alone. To me, it must be a combination of medical knowledge and emotions, since each dog is different both in character/temperment and medical issues.
One thing I have learned in my time with greyhounds, is that their desire to live is unequalled! It is that desire for life that does make them good candidates for amputation and brings them thru many trials, not just amputation. (Darcy: you are a hound, so that counts )
I am not sure why you are fixed on life after amputation? (maybe I need to go reread your posts) There is no guarantee that any dog will live "X" amount of years. The last I spoke with Dr. Couto, the average was still 14 months. Some go more, some less. What is important, to me, is the quality of the time spent after any major operation or illness. If they are happy, that is all that counts.
Winslow's owner, Glynis, asked me to post in this thread, the following:
"Winslow, 21 months post amp. Pain free and happy".
Our friend Queen Winnie lived another 3 years.. pain free and HAPPY.
Jaxen in Canada is 4 years post amp. Pain free and HAPPY.
Darcy, 1 year, Pain free and HAPPY.
And all the others that I've missed or don't know about.... Time spent... PAIN FREE AND HAPPY