I think the science actually supports this. Studies have shown leftists tend to be more self-critical and are concerned for the nuances - the "shades of grey". So their memes must cover more angles of an argument to be effective. Right-wing are more black and white thinking, and don't question themselves once they make a decision. So their meme's are straight to the point and simple (and usually so full of logic holes and lacking in comedy that leftists say: "the right can't meme").