By your very logic, it should be fine to release or terminate people by e-mail. I would bet that if the tables were turned, and Calacanis had terminated Evan by e-mail, that Calacanis would be taking even more heat than he is now.

Call me old school, but the best to worst order of quitting (and on the flip side, firing) is this - face to face, telephone, e-mail only if it's impossible to arrange the first or second.