Throughout the history of internal combustion engines there have been attempts to either improve the ignition process through plug design, or at least increase profits for those who promote such improvements, real or imagined. I remember the bad old days of two stroke motorcycles and weak ignition systems, when removing and cleaning/replacing plugs was often a monthly maintenace item. All sorts of plugs were introduced to supposedly deal with the shortcomings of the ignition system, but ultimately it wasn't the plugs that were the problem, it was the anemic output of the coils. These days even stock coils are more than aequate (thanks to things like EPA regulations that force manufacturers to certify compliance with standards over a minimum period of time). But in an era when the plugs a manufacturer installs at the plant can easily go 50k to 100k miles, plug companies have to try much harder to find ways to sell more product to meet corporate objectives for ever increasing sales and profits. Thus you get the ridiculous claims for what amounts to snake oil from the folks like Pulstar(sp?), or the equally ridiculous products like the Bosch with four ground electrodes.
Once you get your 12% increase from Pulstar, then get one of those vanes you install at the throttle body intake for another 10%, throw a Fitch calalyst pellet in the fuel tank for another 5 to 10%, etc. Pretty soon you will be getting nose bleeds from the G forces when you whack the throttle. Or more likely you'll just have a lighter wallet which will translate into a better power to weight ratio.
The real advantage of premium plugs with platinum or iridium electrodes is longevity. Thanks to the erosion resistance of those materials, the electrodes will remain sharp longer, which reduces the amount of energy required to produce a spark. So you can say that they maintain the level of performance longer than standard plugs. But they don't add performance when compared to a new standard plug. As Twolanerider mentioned, a tiny difference on an inertia dyno does not mean anything.
Anyhow, as long as there are believers out there the spark plug folks will be happy to sell them plenty of snake oil. It is, after all, what makes our economy run, consumers wasting money on stuff they don't need.
Jerry