There are different types of launch control, the kind mentioned above is called a 2-Step rev limit, and isn't really technically launch control at all. Launch control works very similar to traction control, which does an ignition retard (or lowers spark energy, or closes a drive-by-wire throttle) to cut engine power in order to fight wheel spin. So basically you plant your right foot and it takes care of controlling the wheelspin for you. This is not usually done on common street cars because there isn't usually any way to feed individual wheelspeed inputs into the ECU to do speed/power feedback. Usually each driven wheel speed is both compared to one or more of the undriven wheels speeds, and there is some feedback involved. There are crude forms though, which are more common and just compare vehicle speed (transmission output speed) vs. RPM, and adjust accordingly. This can be done in a lot of the aftermarket tuning software for stock ECUs, along with the 2-Step rev limit. The speed sensor input usually goes into the ECU anyway, so not that hard to do a simple version.

You can think of it this way: Launch control helps you launch effectively, and a 2-step rev limiter helps you launch consistently.