Basil Moss - yep I agree about the proportionality. We have short cranks when we get our first bike as kids and they get bigger as we get bigger - up to a point and then they stop. Same with wheel size - but that's a little more difficult to solve.
wanlogan - custom Zinn titanium frame too - so it's built around the custom cranks and has a higher bottom bracket to accommodate them. (it's my dream bike) So no problems at all with clearance - same as for any other road bike. And RE pro riders - don't know what they have - but I believe that Magnus Backsted had a set of Zinn custom cranks - 190's I think. He's a bit taller than hincape & wiggins.
Chasm54 - Yep - definitely can push a bigger gear. Does slow your cadence - but only for a while - until you get used to the bigger pedaling circle. Proportionally it's the same sized circle as a smaller rider would ride with say 170's or 175's so there should be no difference in cadence ability. But I hear what you are saying - and it did take a bit of getting used to - but my cadence is back to where it was before. I completely disagree with you on the acceleration though. It's one of the key benefits imo. I can now accelerate way way better than before - and thats because of the greater leverage. Accelerations that used to spit me out the back are now handled easily. And climbing is way way better for the same reason. I race regularly and since getting this bike I've jumped up 2 groups to now ride in the B grade - and have won the most improved rider award in my club as well as our summer series of racing (I've even had a couple of people question whether the long cranks are legal as they are giving an unfair advantage). I think the key is that I can finally use the leverage advantage that I have as a taller rider - the long cranks enable me to use that advantage. And I've had absolutely no problems at all with my knees jumping from the 175s to the 210s (and I'm currently riding about 350kms / week). Zinn does make shorter cranks for shorter riders - they are all about proportional length cranks - but the video was focusing on tall riders because it shows the proportionality argument better I guess (It's Lennard Zinn in the video I think - so I guess he's a cheap model and is 6'6")
So as you can see - I'm a zealot! But for good reason.
Adrian.