It is neither extortion nor underhanded, nor dishonest if the employee openly and honestly negotiates it before leaving. Unless their contract explicitly has termination penalties if they quit to early (fairly rare in the software world), then they have every right to threaten to leave immediately if they are not given what they want, and this remains honest.
Now, you may have a point with it being disloyal, but what have you done to earn their loyalty? If you or the company has done something unusual to earn their loyalty, then you may have a valid point and reason to feel wrong. But paying them an honest wage for honest labor is not a way to earn any exceptional level of loyalty.
Not to mention, how many people are without jobs? Some people would be grateful to have a job, even with NO vacation.
At the risk of sounding somewhat cavalier, the overall unemployment rate has nothing to do with my situation or my relationship with my employer. The unemployment rate in my particular region for my particular industry matters somewhat, but if we are talking skilled software developers that is relatively low. Even then, the really relevant question is how easily can the company replace me, which includes my specific domain knowledge and my skill level. It sounds like the article was written by someone who could not be easily replaced for people who could not be easily replaced.
To me, your value diminishes rather quickly when you prove to be underhanded, disloyal, dishonest, etc.
Not to mention, how many people are without jobs? Some people would be grateful to have a job, even with NO vacation.