Apparently they have pretty consistently observed that, in freeway situations, using lights creates more chaos than it solves. For that reason, they have a (de facto, at least) policy of not using lights when they need to get somewhere quickly on the freeway. Surface streets, of course, are an entirely different story.
I can certainly buy that argument. It just seems very much less-than-optimal, however -- if people weren't stupid, they'd be able to use their lights and issue a warning, and it would be safer for everyone involved. So perhaps we need to do a better job of educating new drivers about what to do when they see lights behind them. hmmm.