Not "all" real fights, but many: About 60% or so goes to the ground is my guess, not counting sporting fights, and a higher % involves grabbing.
Of all fights I've seen in my life, from highschool to my now 28 years of age, I have never seen a fight go to the ground. Sure, I've seen one of the people fall to the ground, and then perhaps followed by kicking or some such, but I have never seen the situations described here, where the fight turns into a ground/grappling game. Sure, it's not like I've seen hundreds of fights in my life, relatively few really, but still, never seen it go to the ground.
I remember reading a thread here somewhere, fairly ancient if I remember correctly, that took statistics from police reports done on it. From what I remember, the number was something like 10% of violent incidents went to the ground. Since I can't seem to find the thread again, though, take that number with a grain of salt.