Gladwell is more or less in the self-help genre. Is there any self-help book that is really helpful?
He is also an amazing success. Many people are unamazing successes--the woman who takes over her mother's successful business, for example. But look at how many amazing successes (Walt Disney comes to mind) are apparently shallow, inconsequential, childish and so on. People like them, so they're successful. Liking is always a mystery.
If Gladwell has a steady, serious point, he would be like Dale Carnegie: the supporter of some ruthless conservative myth. By jumping from view to view he retains the charm of the self-help genre without its nastiness and pomposity.
He is part of the New Yorker culture: people who can write charmingly about anything, and have honed that skill for generations. He's not the only New Yorker writer whose charm sells his books, but he does seem to be the most envied one. Who knew that being just a little more serious than James Thurber could make someone so much money?