I'm ambivalent about this. A few times in the article the author suggests that only in a small percentage of cases is job-hopping justified, but I think it's actually justified in far more than a small percentage of cases.
The fact of the matter is that contemporary work culture is (for better or worse) progressing towards lower job security, and more job hopping is an inevitable consequence of this. When job security goes down in the economic community, the propensity for job hopping goes up--even when employee's jobs are not directly at risk. This is a natural and rational response to low job security.
Judging workers who have job hopped in the past can be unfair to those workers, especially when many companies are decreasing their own loyalty to their employees. Why shouldn't workers chase higher paychecks outside of their current companies, if those companies don't adequately value their worth? If an employer has not demonstrated a commitment to retaining its employees, it shouldn't expect any commitment in return.
That said, I do agree with the fundamental sentiment behind the article--that companies who are loyal to their employees should prefer employees that will be loyal to them in return.
I think you raise an interesting point. At a time when companies are so ready to shed unneeded workers, it should come as no surprise that employees are less loyal.
However, I don't think that's the point of the article. The author is saying "I'm a businessman, and I've learned not to hire 'job hoppers', and you shouldn't hire them either." He's giving advice to other employers, and as such, he doesn't have to be 'fair' to the job hoppers. From his perspective (and that of other employers), hiring someone is a considerable investment (estimates vary, but between 30 and 40% of annual salary seems to be common). Having made that investment, no one wants to see it walk out the door 2 years later. It only makes sense for the employer to look at an individual's job history and form an opinion about whether they are a good risk. It doesn't really matter why you left six jobs in the last 10 years - your reasons only have to satisfy you - from his perspective, you are not the person he wants to invest in.
As I see it, if you like to change jobs frequently that is your business. You should do what you want to do, and accept the consequences (that some prospective employers will consider you too flaky to take a chance on). But don't turn around and complain that people aren't willing to take a chance on you, and won't give you the job that you now think is the perfect one for you. All other things being equal, if you were the employer and had a choice between someone with a track record of 'job hopping', or someone who seemed steadier in their employment history, which would you choose?