Because Google and you are not setting out explicitly to build a set of links to copyrighted material against the wishes of the copyright holder. It's all about intent. If I go to a high-street store called "Kitchen Goods" and buy a knife, that store's fine. If I go to a store called "Jay's back-alley shivs" run out of the inside breast of his raincoat between 02:00 and 04:00, he's probably not fine.
The law recognises intent in most situations, and the Pirate Bay exists to provide access to expensive-to-create content without compensating the people who made it. Hence, they have problems (and justifiably so).
Actually, in regard to the Appeals Court, its the majority usages of the site that count. If your blog's comments is mostly used for illegal activity, you are guilty of facilitating the crime by having said blog. Intent was not mentioned by the Appeals Court to have any baring on the matter.
This is how they said Google was not guilty, but the pirate bay was (they mentioned Google specifically in the question and answer).
The law recognises intent in most situations, and the Pirate Bay exists to provide access to expensive-to-create content without compensating the people who made it. Hence, they have problems (and justifiably so).