Whiteboard Videos

Lately everybody seems to be making hip web videos explaining things on whiteboards:

I like this trend, since the whiteboard approach seems to help people enhance their presentations with graphics while avoiding full-on PowerPoint-driven slidesanity. But it surprises me that these presenters seem to actually be drawing complicated graphs on actual whiteboards with actual markers. Surely it’s easier to render some of these graphics digitally? Perhaps it’s harder than I think to set up a poor man’s greenscreen? I wonder.