No, it's not a "ploy", it's the only realistic action google could take. It would be a huge business mistake to ban malvertisers from adsense, because those would move to other networks, which would then in turn be preferred by publishers because that's where the money moves. Adsense would lose, and the consumer wouldn't have won anything.

The publishers aren't innocent at all. They decide to place ads right above, below, and all around the real download button. Because they know that a good percentage of their consumers will be tricked, and so they get payed.