That's your problem for friending those people, not the networks for showing you what you explicitly asked for (not duckface pics but posts from those people).

And what makes you think if as many of your Facebook friends were on Google+ (and used it as actively) you still wouldn't see "as many duckface pics" in your feed?

Having said that, I am more confident Google would address the problem and come up with a better method of filtering duckfaces that facebook. Whether they let you toggle the 'duckface filter' feature is another issue.

Yet.