Okay well please excuse me if it comes off weird, I've been up for 35 hours and am heading to bed now.
The purpose of cross-drilling/gas slotting is to allow brake gases to escape faster. These gases would normally push against the motion of the calipers and therefore reduce the effectiveness (brake fade). 99% of street driving does not involve braking that is hard enough and from high enough speeds to warrant that kind of brake cooling. My driving is entirely stop-and-go city driving and I have only experienced brake fade once. The one occasion that I did was when I was flying through a residential area at 3AM at 70+ MPH, constantly on and off the brakes. But seeing as how most people don't do that frequently (if at all), why spend the extra money? Ricers do it because it looks impressive. I doubt they know what it is for. Oh and yes, I do know that despite the reduced swept area, the brakes are still just as effective (friction is not related to surface area).
*SIGHS*
