The question is more one of how much of an actual change can they impart (and under what circumstances?) given the size limitations of something like a wrist strap. My hunch is that this would need to be a fairly large system (including its power source) to have a meaningful impact outside of sedentary activity in an environment which is mildly under/over temperature. So good news for people who get chilly working long hours in their cold offices (which is a completely viable market), but not for runners looking to shed gear. Maybe there's something there for cyclists though, but only if they're willing to put up with a wheel generator.
Also, humidity impacts comfort largely because of its impact evaporation rates. Reducing body temperature reduces the rate of perspiration, in turn reducing the impact of humidity. You're right that it won't eliminate the effects of very high humidity, but it would reduce them.
From the article i understand that it is a nervous system trick: "The research suggested that anything with a temperature change greater than 0.1 degree Celsius per second would produce the effect".
Things like painting roofs silver or insulating buildings are great starts to reducing AC use. (Dark roofs can reach 66C to 88C in hot weather, better roofing helps a lot. (http://www.epa.gov/greenhomes/ReduceEnergy.htm#advhome))
But this? I'd freakin' love to try something like this. I'm almost always too hot, even in England.