The crux of the argument is that Ueli has no proof of his summit of Annapurna. He has said all along that he was caught in a small avalanche on the way to the summit, and lost one of his gloves and his camera in the process. As a result, there are no summit photos to back up his claims. He also says that his altimeter broke during the ascent and that he didn't use a GPS to track his progress. All of this means that there is no solid evidence to substantiate his claims of having gone to the top, which in turn has now led to some to say he should not have been nominated for the Piolet d'Or at all.
In Ueli's defense, his teammates on that expedition, including two Sherpas who were support in his efforts, say that they saw Ueli just 200 meters below the summit that evening, with his headlamp moving steadily upwards. They fully believe he accomplished what he said he did, and don't question his accomplishment at all. Miss Elizabeth Hawley was also satisfied with his summit report, as were French climbers Stéphane Benoist and Yannick Graziani, who made a similar ascent a couple of weeks after Steck.
For his part, Ueli says that he doesn't particularly care what others think, he climbs for himself and the joy of the sport. He is quoted as saying recently “What happened is partly my fault. I am not someone who likes to brag because climbing brings nothing to humanity," indicating that while he doesn't have any evidence to support his claims, he also doesn't have any incentive to lie about either. Want further proof? An article questioning his summit has been posted on his own official website.
I am not surprised that this controversy has reared its head at this time. I predicted last fall that there could be some backlash against Ueli over the lack of summit photos, and that prediction has proven to be true. Steck fully acknowledges the lack of evidence, and doesn't seem to be especially bothered by those that are questioning him. Personally, I'm of a mind to believe what he says, as I don't see what he has to gain by making a false summit claim. He is already one of the best known climbers on the planet, and is past exploits have been well documented or witnessed by other climbers. The fact that Ueli's teammates believe that he reached the summit of Annapurna says a lot as well.
Controversy has long been a part of mountaineering, and it remains so even in the 21st century. Whether or not Steck deserves to win the Pilots d'Or isn't up to me to say, but I do think he has at least earned the benefit of the doubt in regards to his accomplishments.
Meanwhile, Ueli isn't letting these questions slow him down. This past weekend he climbed three classic routes in the Alps in a single massive push. He and Michi Wohlleben topped out on "Cassin" at the Cima West, "Comici" at the Grande Cime and "Innerkofler" in succession, and during the winter no less. The man known as the "Swiss Machine" continues to impress.