That makes a strange legal argument, though. You can't say that Apple putting the default up for bid is anti-competitive behavior by Google. So would you say that Google can't bid in the auction because that in itself is anti-competitive? That also seems like a tough legal argument to make (though I am not an expert on this) because it means that basically everybody is allowed to be in the auction except for Google.

You could definitely say it was anti-competitive if Google was paying more than they earned from this search traffic. But I seriously doubt they are doing that.