Fixed gear touring. Why? That is a good question. I originally started riding a fixed gear for the simplicity of the bike. The bike I currently ride on my 40-100 mile rides actually doesn't have breaks on it either. You would think that might be very dangerous but in fact it is perfect for long rides on designated bike trails. I have no problem slowing down by using leg pressure on the pedals as they continue to move forward. I can guarantee that I am a better biker (control, fitness, balance) due to riding a fixed gear bicycle. You would think that going up hill would be the hardest but actually going down hill is killer since you can't coast and continue to spin. When going downhill fixed with no breaks controlling your speed with your legs gives you one hell of a workout. Your senses are ultra heightened since you would have to avoid anything that might get in your way and not squeeze the breaks to stop.
Now, I might not take a fixed gear to tour the Rockies. You are correct, it would be limiting but it wouldn't be impossible. Keep in mind that the Tour De France was originally raced on fixed gear. Maurice Garin won the tour in 1903 running a 52x19 with no break.
But in the end I think for me it is the challenge of the ride. Riding a 100 miles on a geared bike is easy compared to riding it on a fixed gear. Just think how many times you coast on a geared bike. If your moving on a fixed gear then your legs are working. Riding 300-500 miles fixed over 5-6 days would be a dream come true for me. The physical aspect of it is what really apparels to me I guess.