screencasts are not searchable
False. There are users searching for someone to show them how to work an app rather than a specific feature.
One can argue that a well designed app shouldn't need that but then one ignores how something as common and design understood as cars often require a school for people to even know how to get the thing to run.
Even for simpler applications, just because it's simple doesn't mean people get it if they don't grasp the concept and purpose.
the pace is slow
Every type of help section is slow.
Wading through poor and ignorant customer service is slow.
Wading through help files jumping from features to features just to get an animation in your head of how you can use the application is slow.
Asking around forums, registering and then hoping you don't get flamed is slow.
Even FAQs are slower because these things can skip such basic things as what the application is about when the text description isn't enough. (and assumes you know universal things such as logging in, follow, what not to do to ruin your initial experience, etc.)
I can't jump to the one bit that I am interested in
You can. Annotations/frame buttons/etc.
The point for the user in need is why would they?
There's a reason they want to look at the video and not just half of it. If you mean for further reference or rewinding then that's where the video helps give the user the confidence to understand the help manual better.
Heck even for image manipulation programs I have rarely seen a screencast be more useful than well annotated screenshots...
It could be because you had less problem learning the basics or had someone guide you through it.
For someone like me who doesn't know how to do the most basic of things like cropping, it took a screencast or a video to really help form that image in my head.
No matter how I read the text or see screenshots, I just couldn't get the basics down especially when you combine them into steps.
A screencast affords me an easier way to visualize the real time ramifications of what's happening in front of me and why someone might do something first and then do something next instead of just a bunch of isolated features.