Its not the quantity of facts that a present, but the number of facts you retain. Even more to the point, its what and how much you can do with them after the event (be it reading an article, watching TV or going to the speech). You could watch a news bulletin or read an article and it be a complete waste of time. For a speech that you have paid to go to, its likely you will have gone away and have learnt something useful. Even better you can return inspired.
Hold on, are you telling me people can't be inspired by the written word?
I agree that the number of facts retained is more relevant than the number of facts present, but you've given no evidence that people retain more facts from listening to a speaker than from reading an article (to simplify the issue grossly). Why is it "likely that you will have gone away and have learnt something useful"? You've just rephrased your argument.
Do a little research on learning styles - the methods by which people retain the most facts vary person to person.
Having someone in person tends to be more inspirational than simply reading articles by them, well for most people anyway.
I have actually read up on learning styles - well its a little lie, in fact I downloaded a load of audio programs recently. The thing with an article is that it only caters to one type of learner - the visual type. In order to learn really you should be combining several types of learning, and above all you learn best when relaxed and engaged. A targeted speech has so much more of an effect than an article which may or may not have relevant facts in. Especially if its one of several 100 you need to read.
One big thing I have missed off though is the conversation you get with fellow delegates/audience members. Again, they aid the learning process.