That's some good theoretical info, however, you can't base real world performance on that info because of a few key elements...
For one thing, the whole spark path through the spark plug is not made of Iridium or Platinum. On most platinum plugs the center electrode is only coated in platinum, it's still copper under the coating, so you can't expect a high drop in conductivity.
Also, you're not taking into account the design of the plugs. The plugs would have to be made exactly the same, but using completely different metal (not a combination of copper and another metal) to find extreme differences.
The Iridium plugs have a very very fine tip, which is what is claimed to make the spark jump a lot easier than regular copper plugs. I can't truly back this up with any real testing, but this is the reason that they are supposed to use less voltage to make the spark jump through the gap. In any case, the fact that they have a different design means you can't compare them only with the metals' conductivity numbers.
Finally, here's some REAL WORLD measurements...
this guy took a bunch of used copper plugs, new copper plugs, used platinum plugs and new platinum plugs, and measured their resistance... if what your info says were true, there would be a HUGE difference in electrical resistance measurements. There isn't.
He also points out how, if the platinum's resistance was 10 times higher than the copper plugs, assuming 35 000 V from the coil, there would be a loss of about 120V... 120V from 35000V... not a big deal if you ask me, and this is IF the resistance was actually greater, but it's not.
With the Iridium tips you can argue that the tip itself is actually made of Iridium and not a copper core coated with Iridium... I still doubt it would make that much of a difference, however, there is still the matter of the design to be taken into account. You just can't compare only conductivity numbers with two different designs.
I don't have data to support the claim that the spark jump takes a lot less voltage to accomplish with a thinner tip, but I do believe it. Why? Because I know how my bike reacted to the Iridium plugs.
When I first got my bike it was too hard to start and the battery would drain trying to start it. I got an MF battery and it was still a bit hard to start but the battery could take it. Then I got a new set of copper spark plugs... now I had good battery and new cooper plugs... it would crank for 2-3 seconds and start right up. I considered this to be good starting. I changed the still new copper plugs (doubt they had even 100 miles on them) for Iridium plugs and tested the starting... it started as soon as I pressed the start button, not a second of cranking. This is real world experience right here, which is what really counts in this matter. I don't think there's anything that could have been done better to ensure a good comparison of spark plugs than what I did... both the copper plugs and iridium plugs were new, there was a new battery installed before any of the spark plug changes and nothing else was changed. It was even done on the same tank of fuel. So I say the design actually does what it claims to do