I think the problem I have with the magical device is the fact that it promises the same life expectancy for everyone, but it doesn't equal the 'playing-field' for everyone, people born with severe disabilities would probably just be made to suffer.

Also: To take this further: you said in a comment above the magical device would compensate for additional medicinal advances and thus further raise the life expectancy, my cynical heart tells me that people probably wouldn't want to mess with that anyway (if it were in a whole world scenario) since people are a) scared of change and b) very complacent.
And if it were a country to country issue... how would you determine when someone would die? Would it be done by the countries people were born in? Where they live? In their DNA (if so- what of children with parents from different countries?) Because I can just see a stroves of people rushing to those places where life-expectancy was highest and the countries with the lowest life-expectancy becoming practically uninhabitated.

I hope I don't come across as mean or too literal on this experiment, I do think it's interesting :D *ponders some more*