I suspect he doesn't care much about the storage space. JPEGs make the edges of the lines blurry or noisy - they're designed for things like nature photographs, not sharp hard edges between single-color areas.
It's not about storage space, is about loading time. When I read it through the connection I have at work, it took about 2 minutes to load.
When it's JPG artifacts in an image best suited for PNG you blame the publisher.
When it's slow loading times you blame the pipes and the piper.