[saurik]

This is a very important point to make: data interchange formats typically much slower to manipulate and require much more RAM to do so, as they will require mapping back and forth to the internal data structures actually used at runtime. If you take a look at an older (pre-"x" formats) Office document, you will find a lot of its complexity (in addition to the aforementioned backwards compatibility and "numerous unrelated features" issue) relates to figuring out how to edit and resave enormous documents quickly.