if the speaker is presenting enough information I'll pay close attention.
if they are taking n hour to present 10 min worth of information I'll listen (to catch the 10 min worth of information) while doing something else rather than leaving and missing that 10 min of information.
I honestly don't care how much time the presenter spent preparing. I care about how useful the presentation is. I've seen cases where someone standing up with (near) zero preparation gave a far better talk than someone who prepared for weeks.
long preparation time does not mean that the presentation is good. different people need different amounts of preparation time to give the same quality presentation. This is no different than in programming where some people take weeks to accomplish what others can do in hours.
some preparation is good, and I have no disagreements with the recommendations in the original article, but don't make the mistake of thinking that since it was hard work to prepare that the result must be good.