Agreed. Screencasts are linear at the presenters pace. Documentation can be skimmed or probed randomly. Often I dive deep to see how a particular issue is handled.

All too often screencast production qualities are terrible: lighting sucks, the cameraman focuses on the wrong things, the pacing is wrong...

Developers are readers. It's mostly what we do: code, documentation, logs, stack traces. We are a pretty literate bunch. OTOH a video of a new tool would be more useful for a mechanic than the usual postcard description.

That being said, good graphics help a lot. I found the Wikipedia sort demos wonderful.