I'm not sure if I am misunderstanding your argument, but it seems like you're complaining about the fact you can't pass "functions" to methods that accept a block? You can! :D
times_two = -> (x) {x*2} # Proc (lambda)
times_two = Proc.new {|x| x*2} # Proc
[7, 13, 19, 23, 31].map(×_two)
Also, if you want to call a method on the objects, you could do: [7, 13, 19, 23, 31].map(&:to_s)
Which is a bizarre syntax, if you ask me (actually, not really if you know how I works in the background, but it still does look bizarre IHMO).
As the slideshow illustrated, it's all about having good taste as an author. Knowing your audience and all that. In fact, that might have been a good point to add to his slides--that different coding styles are appropriate for different teams and projects.