That's the claim made here on Presentation Zen:
By insisting that presenters submit their "PowerPoint slides" for inclusion in a future conference booklet or future download from the conference website, conference organizers force their speakers into a catch-22 situation. The presenter must say to herself: "Do I design visuals that clearly support my live talk or do I create slides that more resemble a document to be read later?" Most presenters compromise and shoot for the middle, resulting in poor supporting visuals for the live talk and a series of document-like slides filled with text and other data that do not read well (and are therefore often not read). These pseudo-documents do not read well because a series of small boxes with text and images on sheets of paper do not a document make. What results from trying to kill two birds with one stone is the "slideument." The slideument isn't effective and it isn't efficient...and it isn't pretty.
Garr Reynolds suggests that speakers get around the problem by making two sets of slides: One for the conference book, and one to use for the presentation. It's a good idea, but I wonder how many speakers will make the effort to do it?