This is not true and suggests that the author has limited experience dealing with the general population. The college going population is not the general one, and even within that population there are huge differences in ability. This is like saying that UC Berkeley and Cal State San Jose are not meaningfully different in their student intake.
I think you're talking about a very different kind of "ability" than I am. Some kids, coming out of high school, will know calculus, or have the ability to play an instrument, or the ability to render the human form in an anatomically-correct fashion. They also might know any amount of trivia--a list of presidents, the names of all the bones in the human body, etc.
None of that knowledge is really representative of being any "better" at anything. They may have just spent less time on the basics, and more time on the advanced stuff. It might just mean they were pushed to take more credits by their parents. They will likely have fundamental gaps (the inability to multiply two numbers in their head, for example) and rely on crutches (like a calculator) to keep up with everyone else in the advanced classes they're forced to sprint through. They might have done it all through rote memorization, and have no clear idea of what any of it means. Recall the refrain of most medical students: "I don't have time for the lesson; just give me the formula."
This is in opposition to the people who are "just better" at the fundamentals: each new thing they set out to learn, they'll learn faster and better, because they'll be building their new knowledge on top of mastery rather than a shaky 60%-and-move-on foundation.
You might wonder about IQ: IQ or "g" is literally the measure of how fast you can recognize and employ new patterns, and therefore how fast you'll master new micro-skills. Kids with higher IQs will do better under time-constraint. But given as much time as needed, and assuming mastery of previous subjects, IQ is irrelevant.
An amusing visual analogy: when you master a micro-skill, you've cleanly filled up a line of blocks in the "well" of your knowledge. When you master enough micro-skills, leaving no "gaps", the knowledge comes together and compresses: you get a Tetris. :)
It's part of how IQ is defined. IQ is literally just "the (population-normalized) number that comes out of IQ tests", and IQ tests are structured as a set of pattern-matching/lateral-thinking questions which must be answered under time-constraint.
Everyone can recognize a pattern or get a lateral thinking puzzle eventually. Adding the time-constraint splits the world into people who can recognize patterns quickly enough to employ that pattern-recognition in the course of their every-day life, and those who can't: thus, IQ. Without the time constraint, an IQ test wouldn't really measure anything at all.
IQ is believed to relate to intelligence because the ability to see patterns sufficiently quickly gives you a kind of "intuition" for new subjects. It's like a lubrication against friction: without it, new subjects will be "at rest" in your mind, and you'll have to give them a push to get your understanding of them going. With it, they'll just slide down the funnel right into your brain. :)
More technically, IQ could be seen as a measure for how much of a cost your brain puts to engaging your type-2 reasoning (http://lesswrong.com/lw/531/how_you_make_judgments_the_eleph...). As expected, glucose, butter, CNS stimulants, and other things that make the brain think it has more "stored resource" to work with, are measured to enhance IQ--because they lower the brain's calculation of this cost, and therefore allow you to engage your lateral-thinking processes more easily and more often. Likewise, hunger, depression, and other things which raise your brain's cost evaluations unilaterally, also raise the cost of engaging your type-2 reasoning, and thus lower your IQ.
which have no time limit, yet are very difficult. I don't think "everyone" has the ability to answer all of these questions.
"Without the time constraint, an IQ test wouldn't really measure anything at all."
It may measure how well you are able to abstract problems.
Whether or not it has much to do with your ability in different disciplines is another matter, but arguing that it is simply down to timing seems somewhat silly.
You're still implicitly assuming a time-constraint, though: the amount of time the person is willing to put into the problem before giving up. Presume someone puts in years of thought to a single lateral-thinking problem, and yes, they'll get it. Anyone will get it, if just by raw brute force, testing over every possibly combination of properties of the system that might have an underlying correlation. Most people just aren't willing to do that.
Given a finite amount of patience (or, equivalently, a time-constraint, which sets "patience" to a known quantity instead of allowing it to vary per individual), we can give a person an infinite stream of unit-sized lateral-thinking problems, and then see how many will be solved correctly before they "hit the wall." This is then a measure of their ability, in general, to recognize patterns quickly enough to put these insights to use: IQ.
None of that knowledge is really representative of being any "better" at anything.
I don't see how this differs from denying the idea of better, full stop. Half of my secondary school class were better at calculus than me, as measured by our leaving exam. It's a noisy measure but our rankings were related to true mastery of the subject matter.
* Kids with higher IQs will do better under time-constraint. But given as much time as needed, and assuming mastery of previous subjects, IQ is irrelevant.*
Citation needed. I did not really believe that my relatively crap math ability was far above the average until I saw someone spend two hours getting tutored, one one one and still not understand the idea of a vector. I'm sure they could have been trained to mechanically perform an algorithm if they could recognise the class of problem, which is also pretty hard, but they were not going to get it, ever.
[1] http://en.wikipedia.org/wiki/Regression_toward_the_mean
This is not true and suggests that the author has limited experience dealing with the general population. The college going population is not the general one, and even within that population there are huge differences in ability. This is like saying that UC Berkeley and Cal State San Jose are not meaningfully different in their student intake.