I'd always add to my spiel...
"... and if you feel the need to talk through the presentation, as you have done though my introduction, please exit now through the doors to your left.." :wave:
Usually not, and then I would approach them and ask them to be quiet during the show - or, I would use my line from above and if that didnt shut them up - I would pause and stare and wait, which usually prompted other guests to "Shhhhh" them.
I, like most people, get annoyed by guests talking throughout a show or ride. But to tell you the truth, if I were at WDW and I witnessed a CM handling it the way you describe how you do it, I would find that CM very unprofessional. Surely there must be better, more "Disney-like", way's to handle this type of situation.