The problem with graphs in the first post is that the data they present is too discrete. Aggregation makes for much better visualization and generalization.
To that end, we're going to take the 24 768x512 images of the
Kodak image set and the 8 1680x1200 images of the
Jpeg-XR test set ask the question "how much space would one save if a
batch of Photoshop jpegs had
each of its images encoded by something else?". The effect is that gains on each image is weighted against how much space the gains would actually save. Using Photoshop batches as a reference point also assumes that constant quality encoding is more important here than arbitrary size limits.
TL;DR: Jpegs are gonna stick around for a long while.