This is an amateurish and exceptionally stupid strategy, and a poor way to conduct business. It amounts to acting in bad faith, "Gotcha, hahaha!"
What goes around comes around. Reputation and trust are valuable, if not everything. They're easy to break and difficult to regain.
All to save a few bucks, when he is the world's richest person? Seems just a tad greedy to rip-off / shortchange the proles.
I've never seen it come around to bite those who do it though. The problem is one of power - the people affected typically are those earlier in their careers with less opportunity to say "no" to what looks like good employment, only to have part of their pay calculation ripped out with no warning.
In the case of the CEO/CTO, it was even worse as the company was in talks for acquisition and the firing for equity ended up netting the CEO an additional six figures within a few months. And they certainly seem to be doing fine.
I've seen a number of those. In one case, the CEO fired the CTO right before the one-year cliff in order to get more equity, then invited them back on in an advisory role for 1/10th of the equity compensation. (they did not accept)