There are other aspects. For example the amount of data which is squeezed through the lines or through the air to deliver a page.
The article Lightening Your Responsive Website Design With RESS and the related articles linked in the "Editor’s Note" at the top of the article describe ways to get pages loaded faster. On the speed field Moodle also needs to improve a lot.
But talking about techniques how to make Moodle work on screens of any size or to shorten the page delivery time is not enough. The most important part is a mind shift on the developers and theme designers side. To understand that there is no default screen width any more - only a wide range of possible and not predictable page widths.
The magic word now is less, less KB for the images, less JavaScript on the client side, less bandwidth to deliver content, less knowledge about the screen size the content will be shown on etc.