Oh man I love heights, I'm scared of stupid things like being responsible or paying taxes.
edit: I know that sounds really BS dumb of me to say that. I am amazed at the balls those two climbers have and I am no way trying to claim I could do it. But I would like to try. Obviously I have not actualy climbed that tower or anywhere near that height but I have been in situations climbing on similar structures at 50ft or more many times. Not to mention much high than that in trees as a child. Rock climbing is a good example of blocking the fear of heights. Above the fatal fall point it's all the same risk.
Your space needle experience was different. You were trusting the engineers skill who built it and not risking your life with your own skills. Such as riding on the back of someone's highspeed motorbike, it's no fun when you're not in control, it's just scary. You know you can fly a plane, so at the controls you feel at ease. Those guys know they can climb those ladders. No doubt eliminates the 'fear' of heights.
It's totaly mind over matter, climbing at anything over around 50ft is going to kill you or seriously cripple you if you fall. It makes no difference how high you go above the fatal fall marker. Obviously the fear will be many times greater from the placebo effect that falling from 1500ft will be worse for you than falling from 50ft. But really that is not the case, obviously. Some people have fallen of a chair and broken their spine where as others have fallen from 30k and survived. Above a fatal falling height it's all pot luck.
Imagine a tight rope 50ft in the air over concrete between two poles. It would be certainly very serious if we fell and so the fear would stop us attempting it. If the same rope was over water, we would probably all give it a go as falling would be unlikely to injure us.
It even effects our motor skills. Nature is telling us to stop climbing because it thinks we are going to die. It's a survival instinct. Sadly if we are mid-climb nature didn't think about the fact that stopping us from climbing upwards any further also prevent us from climbing back down. We lock ourselves to the object we are climbing and refuse to move an inch. That is the fear that has to be overcome before attempting anything as crazy as that video. With no danger invovled we could easily navigate the thin ladders, with fatal danger the fear will make even a set of stairs with a handrail seem like a death trap.
batfink's guide to not being afraid of height Vol 1

summary: above 50ft youre screwed anyway so enjoy the extra exhileration the higher you are.
That video was unbelievably awesome, thanks for posting madda.