Uhh, I agree with you ... I said PNG is the best option because it is. That doesn't mean I don't think other options should be available, which is why I suggested zip. Also, jpeg would another option.
As for how many times you've "told me" ... well, that was the first.
And I know PNG won't compress further, that wasn't the point If you read again is said "so you don't have to use PNG." Which means, other formats beyond jpeg, etc.