This seems a perfect moment to point out the less-told side of Reinhold Messner's incredible feat. Not only is he the only one who summited Everest solo and without oxygen, but he also did it from the more difficult Chinese side AND in August. One of the few truly superhuman feats in human history, Messner was the only soul on the whole damn mountain.
But there's a certain logic to the madness. Large teams mean large, sluggish logistics on foot, it takes 2-3 weeks of moving supplies up towards higher and higher base camps, just to get a shot to summit from the South Col, bottlenecked in a high-altitude traffic jam.
Alone and with no oxygen to carry, Messner could move light and fast, so he was up and down the mountain in 3 days. His odds for 3 consecutive days in August were just as good than 35 consecutive days in Spring.
Check out Mister Messners Wikipedia page, the man is a living legend for several climbing reasons: http://en.wikipedia.org/wiki/Reinhold_Messner