Sounds like a flawed theory... apart from providing the spark, one of the other things plugs do is conduct heat away. The electrode on the platinum plugs is much smaller than regular ones, so if anything it would be hotter and thus more likely to burn fuel. But then agian they are all categorised in heat ranges to take care of this
But... how does this reconcile with the fact that a turbo car in hard driving mode will be mapped to run rich i.e. more fuel than can be burnt anyway...
If anything, it strikes me the risk might be that the hotter electrode temperature might cause pre-ignition, so if you're runnig na tuned car, best off to run a colder plug, regardless of whether it is platinum or regular.