Those are not the people we're discussing. Those people aren't deciding whether to work 9 to 5 writing java for an insurance company or go work for a startup as employee #1. Yes, you can make lots of money consulting. I spent a year doing nothing but consulting. It's mind-numbingly painful work. Apples to oranges.
But what you will find is startups that are willing to offer their early employees wages fairly close to market rates (though to be fair, we don't know in this situation whether the person in question's salary was near typical market rates, we just know that he was deciding whether to take a 50% cut in it), which is (if I'm reading correctly) what the article is suggesting people look for rather than settling for shitty wages and delusions of Facebook-level growth.
I think you'll find this is much rarer than you think. Most startups, especially YC companies for what it's worth, are offering exactly what's mentioned in this article at that stage. While it's totally ridiculous, it's currently the state of the world. Sure, it sucks, but asking for 20% is going to get you laughed out the door.