It's caused by the "rewind" word. I never owned a VCR but still thought about one :). The software started to use other terms for the action, like "jump backwards" (VLC media player). Probably because the actual rewind action (show the movie backwards very fast) is not easy to do in compressed video (to show the last frame before a keyframe you have to seek the previous keyframe and recompute all the frames until the desired one).
It's too bad that current media formats don't allow you to scrub (at least, the ones I usually come across - I have no idea what makes a compression format "scrubbable"). IIRC, this was one of the selling points of Quicktime.
Only key frames and no frames that are in any way predicted by what came before it. That's actually the major point that differentiates formats intended for consumption and those intended for editing. If you usually only watch something from start to end, you can vastly increase compression ratio by re-using parts of earlier frames that changed very little. However, this means that to get to a particular frame you have to find the last keyframe before that and then decode from there.
