There are a few reasons, one of them is that some people have extra money to spend and just want the best, others need more and consitant stopping power, and another factor is looks. For 99% of the cars that you see and read about, the C5/C6 brakes(nearly identical) will be more than enough, and these days they are dirt cheap.
The six piston baer brakes,wilwoods,apracing, stoptech, and brembo are all great brakes, even if a few of them have different things going for them. IMO a big factor is the "wow factor" most of the PT rides have wheels that show the brakes, and most people like to have the brakes kinda making that "OOOH" statement. These days the brakes can be as a big deal as the paint and wheel combo as they are so visible.
People who are more concerned with going faster actually can utilize the bigger/better brakes, as they give more conistant, grip, and heat resistance than something like a C5 setup. Plus they are usually lighter which helps save unsprung weight. ALso the trick setups have floating rotors which help reduce rotor warping and other things.
IMO the bigger brake setups are mostly a waste on most street cars, or even cars that people are going to track, as it takes a lot longer for a driver to get fast enough to even use the brakes enough to warrant the need for something bigger/better. Its more of a "who's got what" thing. But it probably is the best thing to waste money on if you are going too. Nothing better than having good brakes even if you don't use them to their potential. Thing is that most people think of better brakes = better stopping distance which isn't always true, yeah you will get a better stopping distance but only IF you are that good at braking on the verge of lockup. The key to these higher end brakes is that they won't be affected by heat as much, and will provide more grip and clamping force, all things that prevail under extreme enviroments IE a proficient driver at the track.
If I remember CarlC in his basic/simple yet fast 68 camaro was running C4 brakes with race pads, and had no problems and was outrunning almost everyone on the track, and another guy in a C5 corvette finally boiled the fluid in the car(all stock brake system) not until the very end of the day after making extended passes without any cool off time. Some higher temp brake fluid would of solved that problem, although better brakes will transmit less heat into the system.
So what does this all mean? If you think the C5 brake system Looks good enough for you, it will work just fine and probably beyond what you will need. I would recommend touring classics kit, for the price there is no need to try and piece together for yourself. I have installed a set on a 68 firebird and it worked great.(although they only offered a manual master cylinder)
BTW I would recommend to not get crossdrilled rotors if you plan on putting some heat into the rotors, it took me a long time to finallly realize this, I would never listen, and am guilty of having crossdrilled rotors but in all honestly I now think solid rotors not only look better, but all the morons at autozone won't drool over your "poser rotors" LOL
Edit: and we all know its impossible to do 200mph