I think its safe to say that some subjects are more interesting to some then others. That said, it helps if you are good at presenting stuff. Or if whomever it is you are trying to educate/inform is looking up to you.
I would defiantly say that its way easier for someone to learn something if they CARE, because then they will try to learn as much as possible(within their capabilities). And there are as far as I know two way you can care. Firstly, they might care about the subject whatever it might be. Secondly they might care about what the presenter is saying because they know(or think) that whatever that person is talking about is actually worth knowing.
I guess the presentation part is a little more defuse, but in general if you are good at metaphors/illustrations chances are people will understand more. A good sense of humor and a waste amount of knowledge will also help in persuading the receiver that it is a good idea to listen to you.
I have heard presentations on stuff that I know to be interesting but just didn't care about afterwards, sort of. I've also heard interesting presentations about subjects I never thought I would care about. So in the end it is mostly what the presenter is presenting and how he presents it.
Meh, this is starting to become very obscure so I think I'll stop. That said I'm no expert, but I have seen a fair share of conversations and presentations. I suspect there are plenty more here who have lived longer then me and also know a lot more the me. :stud
sorry about long rant, but I have seen OH SO MANY bad presentations... :\