I'm not sure, but I'll offer an opinion anyways.
Back in college, I used a modulated laser and an osilloscope to measure the speed of light, and it was just about dead-on. I'm guessing that laser tape measures use a similar principle. Bouncing a modulated laser off of an object and then measuring the phase shift of the reflected beam would provide VERY accurate distance measurements as long as there isn't significant signal degredation.
Something to be on lookout for are ultrasonic measurement devices that are "laser guided." Such devices use a laser for targeting purposes, but an ultrasonic transducer for the actual measurements. I have a Craftsman model that came with a laser level kit, and while it's roughly accurate, I wouldn't trust it over a coiled metal tape.