Oh, I get you. And yeah. Think of it like Havok for physics. Rendering lush forests and rich flora requires engines be programmed to accommodate such things, balancing asset streaming, optimisation, lighting across multiple assets, and so on. SpeedTree is a good middleware solution for efficient engine rendering of flora. Saves dev time, and still looks great. The Witcher 2, for example, uses SpeedTree.
It takes just as long to make a plant as it does to make a bench. But there are millions of plants, and only so many benches.
Okay. I guess there's middleware for just about everything commonly used in development...