Okay, a sample size of two doesn't necessarily mean anything, but I think there is something to this. In my opinion, the reasons are twofold:
First, unlike most of the "hot topics" in the skeptical community, AGW is goddamn hard to understand. When it comes to creationism, anti-vaccination, alternative medicine, religious and paranormal beliefs, even as a layman I can pretty handily explain why it makes no sense. (On a side note, some of the anti-vaccination propaganda is somewhat harder to debunk, which may help to account for folks like Bill Maher) With AGW, on the other hand, pretty much the best I can do is point out that the vast majority of people with legitimate credentials say it's real, so I have to trust them on it. Of course, it helps that when AGW denialists show the graphs that are supposed to show that warming doesn't track with CO2, I think they show a pretty strong correlation given how noisy climatology data is... but I really don't know very much about the topic, and to be able to guess whether the predictive models are accurate or not, well that takes a lot of knowledge I don't have.
Second, and I think this is important because Randi alluded to this in his statement, environmentalism is a pseudo-religious endeavor for many of its adherents. For those who view it this way, often their goals end up being laudable anyway, but the reasoning is sometimes sloppy or just outright wrong.
A "supersense" of purity is the driving force behind a lot of religious intolerance, it seems. It also feeds a substantial amount of the appeal of alternative medicine: Don't "pollute" your body with those "unnatural" pharmaceuticals. Flush those toxins which are "contaminating" your health. Etcetera.
So should we really be surprised that some skeptics, as soon as they get a whiff of something being associated with a purity campaign, immediately put their bullshit detectors into overdrive -- to the point that it sometimes scores a false positive?
You could even argue that this may have fed into Jillette's ludicrous denial of the dangers of secondhand smoke (which he has since at least partially retracted). When the subject of smoking came up on the denialism blog, I was shocked at how much vitriol some of the commenters had for smokers. It was as if, rather than smoking just being a public health hazard, they thought it was a horrible sin, and that anyone infected with the sin must be an evil despicable person.
I also think a supernatural sense of "purity" feeds into some of the the stricter outdoor smoking regulations... There is no doubt that prolonged exposure to secondhand smoke is hazardous, but it is weird to me that someone who is bothered being ten feet away from a lit cigarette has no qualms about waiting minutes at a crosswalk at a busy intersection. I'm no scientist, but I have trouble believing the former is as harmful than the latter. (Try this experiment sometime: Ride a bike down a fairly busy road where traffic mostly flows at a pretty decent clip, but where there are a number of widely-spaced traffic lights. Smell the air in between intersections, and at the intersections. Mmmmm, that intoxicating scent of exhaust mixed with burning rubber and melting brake pads -- gotta love it!)
So the moral is: As skeptics, we must be careful not to let the smell of zealotry become a primary indicator of trueness or falseness. Though they may be garner the support of superstitious fanatics using fallacious reasoning, AGW and the risks of secondhand smoke are both quite real.