> First of all it's best done face to face, because you don't want to be misunderstood, and you want to give the other party a fair chance at replying.

You're making an assumption here: that one is leaving for amicable reasons (e.g., a better paying job elsewhere, a new career path, going back to school, etc.). There's another mindset that this sort of company is perfect for: "I don't give a hoot about my soon-to-be-ex-employer, I just want out."

In that case, a company like this might even be the better means of quitting -- as the saying goes, "if you don't have anything nice to say, say nothing at all." This company provides (IMO) a valuable ways of communicating without having to get personal feelings involved (at least for the departing employee).