It's no surprise that Ns outperform Ss in these areas. What's the significance? And who says N-oriented tasks are more representative of true giftedness than S-oriented ones?
I agree with you sim.
They measure a
sub-set of skills that we loosely label as academic intelligence.
Those statistics demonstrate that those we label as academically gifted have a higher instance of self-identifying with certain MBTI types. It's circular when you think about it ... the tests, derived from academia, appeal to academia, measure the same academia.
IQ tests are "certainly very reliable, and do in fact relate well to success in school and western society -- i.e. the culture and institutions that share the values of these tests." (prev source)
They have merit, but not without context.
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There are many difficulties trying to measure intelligence; for example as alluded to above, cultural variables.
Here's a farm IQ test for you peeps:
1. How many days does it take for a chicken egg to hatch?
2. What color is a Holstein cow?
3. How many stomachs does a cow have?
4. Does a bull have a cud?
5. Is a rooster necessary for a hen to lay eggs?
The answers: 21; black and white; 4; yes; and no, unless you want fertilized eggs.
These are easy questions if you grew up on a farm! But you'll be sneaking off to Google to look them up if you didn't.
So it is with IQ tests - some assume a knowledge-base which introduces a variety of biases dependent upon your personal history. And although it is widely accepted that tests in use today try to be as culturally neutral as possible, there are many other biases that are difficult to dispel.
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The point: so you do an IQ test and are 130+. Or the school counsellors say you are gifted. It doesn't mean you'll be any more successful or happier in life than those who are closer to the top of the bell curve. And that's not speculation.
Remember, "With great power comes great responsibility."
Uncle Ben. 
