This is the first time I ran into this term "cognitive load" describing the ease-of-learning for a given UI. All the things consultants are inventing, not bad

However, I'd like to point out that low cognitive load, meaning it's intuitive to learn might also mean it's inflexible and frustrating later when you get to use it a lot -> synonymous to not good for power-users

That's something I have seen when observing people actually using WP for a longer time. They are complaining how rigid it is, and it is difficult to do any simple tasks beyond everyday use; for example I found it pretty hilarious that you apparently cannot change the default bluetooth name for the device without connecting the device to zune or whatever, there's no UI for that in the device itself

Of apple devices I unfortunately cannot say anything really, as there are so few iDevice users around here.