Why do emperor penguins breed during the antarctic winter?
From my experience working on sheep farms in Australia, it could very well be for similar reasons to why farmers breed their sheep at specific times in the year - they breed their sheep, so that by the time winter hits the lambs are large enough and have enough wool to make it through. The penguins lay their eggs in the dead of winter, but they then incubate for 65-75 days, by this time winter will have largely passed, and the chicks will be growing in the spring and then summer. By laying in the winter, the penguins avoid exposing their young to a winter for as long as possible.

Another point to consider: As you said, Antartica is largely devoid of other life during the winter. To me, what I hear is: There will be no predators to feed on the eggs, or attack the vulnerable penguins incubating their eggs.

Reference: http://www.antarctica.gov.au/about-antarctica/wildlife/animals/penguins/emperor-penguins/breeding-cycle