Cadel unfortunately just is not a strong enough climber. Having never seen him in person, I can only use my views from photos and televisions, but he looks more like a Classics rider than a GT rider. He seems too stocky (maybe his Chin hides a more lean frame), but unlike Basso/Contador and even Lance now, Evans just seems a little heavier, and it seems to show on the bike when climbing.
He and Basso were using different chain rings sizes in the front and back up the Zoncolon, but, the gear inches were the same, meaning the effort needed to climb was the exact same (all else being equal). Therefore, I can only assume that he had extra weight to haul up the mountain, which allowed Basso to kind of just ride a smoother, more steady pace, while Evans had to get out of the saddle, and will himself up the mountain.
However - I cannot doubt his heart. The guy seems to give more effort than any other rider out there, and so I will continue to root for him in this year's TdF.
The one thing going for him is that the Giro was a tougher course this year, and I think this TdF, with its lack of mountain top finishes and less steep climbs will benefit him compared to the Giro.