Hmm, it seems that we have a typo in the comref
Anyway, how did you test the command? Judging from your post you tested it from a init field?
Init fields are never a good way to test new commands, use triggers (or scripts) instead..
It works for me fine (ArmA 1.05), didn't test on human driven vehicles though..
And 'fine' is a bit relative term because it makes the vehicle (AI driven) to slow down but it speeds up again after reaching the
limitSpeed value, so limitSpeed doesn't seem to be very usefull..