Are mp4 bit rates the same as Flash bytes per frame?
Comparable yes but unlike Flash you have a very consistent average size over the timeline of your content. So you don't need to download as much to show content but can actually just start right away to play the video if your bandwidth is equal to (in practice it should be a bit higher of course) the average bitrate of your video. You only need to pre-load a tiny bit to account for inconsistency in the download rate.

Edit: What you have to consider when using looking at the graph you posted, you have quite a bit of very low bitrate frames, so the peak is not really that important, they somewhat cancel each other out. Whats important when streaming is the average bitrate as this is the bitrate that is needed to stream the video consistently without stopping to fill the buffer a bit more.
In reality you usually need a little more than the average to cope with very "noisy" bitrates that go up and down for long periods, your video is already a rather extreme example, usually you have a much smoother graph. It always depends on the complexity of your video to how well you can compress a frame.