"It is a safe assumption that a group of random students at a public Canadian university are not nearly as ambitious as a group of students at an impossibly competitive university such as Princeton."

No, it is not a safe assumption. It remains to be proven, and that's assuming you can even come up with a decent objective definition of "ambition". Your post-hoc reasoning is exactly the type of reasoning that is taken to task in the article -

Gladwell: Making a task harder makes people perform better.

Academia: No, actually, when tested with a higher-powered study, this effect disappeared.

You: (with no evidence, and only after the release of the Canadian study refuting Gladwell) Oh, but the result only applies to ambitious people.

That argument is weak - it's fitting the facts to the hypothesis, and not the other way round. With the available data, the only thing you can really say is that perhaps a study needs to be done to better understand the why the Princeton study and the Canadian study gave different results (statistical fluke? different ambition? cultural bias?)