The discussion of wet grass was more aimed at a question about halfway through the thread, which was regarding kicks like the tornado kick or a spinning hook kick, and that as the ground gets more slippery, the risk of injury when falling becomes greater, or the rules change (i.e. in Olympic TKD you can't grab your opponent's legs) you're going to have to change which techniques you would want to use. This sub-discussion is not about Taekwondo in general, but specifically about the more energetic techniques and whether or not they're practical in the real world.
My dojang has mats. They're never covered in rain or ice, and my feet never get stuck in them like they can in mud. They're never hard like a wood floor or concrete. My opponents have rules they must follow, such as no grappling, no strikes below the belt, no punches to the head, and no knee/elbow strikes. I'm usually wearing pads, as are my opponents. In sparring, you fight a single person in your weight class, which does not always happen out in the world. My opponents don't have weapons in the dojang. I don't have my carry weapon when I'm sparring. I'm not allowed to go for soft targets in sparring, like the groin or eyes. There aren't tight spaces like a hallway or elevator. We have good lighting.
To say that the gym or dojo isn't sterilized is what I'd consider a fallacy. Training sport Taekwondo (specifically sport Taekwondo, as that's where the wet grass discussion started) has a huge number of differences between the dojang and the real world.