Sorry - I want my version control system to be really, really good at being a version control system, not at being a system to train other software developers.
If you're an experienced developer, you should be able to pick up the static source code and figure it out how it was engineered. If you're not as experienced, you will learn through doing (not reading) and perhaps by working side-by-side with a more experienced developer.
If you're a really good developer it is true you might not get a whole lot of value from watching a playback. If you're a really good developer, though, it is difficult to take the time and effort to teach all of your less experienced team members about what you have learned while writing the code and to become better programmers. These playbacks offer a relatively efficient way of letting good developers teach once and have many developers learn.
If you're not a really good developer the question is how do you become one? It is possible to learn the hard way by doing (like you suggested), but it is painful. A playback is not just watching the code as it was developed but it is listening to the developer explain why they are doing things. My hypothesis is this will make it easier for people to become better.
If you're an experienced developer, you should be able to pick up the static source code and figure it out how it was engineered. If you're not as experienced, you will learn through doing (not reading) and perhaps by working side-by-side with a more experienced developer.