1. One of the best communicators I've met strongly suggested never to present from powerpoint on screen, but rather create a brochure to print and hand off to participants. His claim was less that it impresses, but rather that it changes dynamics of "presenter vs audience" and makes it more of a "discussion group / workshop", which tends to be a more productive dynamic, especially in sales/persuasive setting.
2. Alternatively and more prosaically, dear gawd, 99% of people using PowerPoint don't know how to use it. They don't know how the slide show view interacts with a Webex presentation, so they end up sending a small thumbnail to projector, presenter view to remote audience, but hey things look ok on their screen so they keep going. PDF would alleviate some of those issues :P