I look at a fair number of online videos, especially those embedded on blogs. But I haven't seen this feature implemented broadly. It is a wow feature.
Look at the dots above the progress bar: they tell you what topic is being discussed and allow you to jump back and forth between segments. (the particular dot I moused over said "Randy Moss") The video I saw came from this link.
This simple-looking feature is immensely useful to users. You can efficiently search through the audio file and find the segments you're interested in. It's like bookmarks students might put on pages of a textbook for easy reference, except these are audio bookmarks.
Why isn't this feature more prevalent? I think it's because of the amount of manual effort needed to set this up. Imagine how the data has to be processed. In the digital age, the audio file is a bunch of bits (ones and zeroes) so no computer or humans will be able to identify topics from data stored in that way. So, someone would need to listen to the audio file, and mark off the segments manually, and tag the segments. Then, the audio bookmarks can be plotted on the progress bar... basically a dot plot with time on the horizontal axis.
In theory, you can train a computer to listen to an audio file and approximate this task. The challenge is to attain the required accuracy so you don't need to hire an army of people to correct mistakes.
A very simple concept but immensely functional. Great job!