I can assure you that for anyone dealing with large volumes of storage and/or bandwidth of still images (i.e. pretty much any high-traffic website), where costs

I can assure you that for anyone dealing with large volumes of storage and/or bandwidth of still images (i.e. pretty much any high-traffic website), where costs directly related to storage/bandwidth are measured in millions of dollars, will not consider a 20% saving to be a "pretty minor" thing. I agree that in video, the savings can be even more substantial. But keep in mind that the median web page still has zero videos, while the median web page has about 1 MB in images. In practice most of the transferred bytes in web browsing are html (which is very small after compression) and images. Javascript, css and fonts also contribute to the page weight but those tend to often be locally cached since they're mostly static compared to the html and images.