All that's happened is that with the intro of the iPad, the MacBook suddenly seems too big to carry around. But it's not.
To be able to show the client truly anything you could want to show them, whether it be a website in Safari, a 'real' Keynote presentation with all the bells & whistles, or a Photoshop mockup you're working on, a Flash animation or After Effects video, etc., the Macbook is the better option. I doubt the iPad will ever be able to do all these things, even assuming the chips will keep getting faster as time goes on. So far it seems the iPad's video output was designed with young students in mind so as to give basic presentations in class with a minimum of fuss, and not as a full business tool.
But then again, you never know. Your iPhone didn't do all the things you're using it for when it first came out. Stay tuned.