This isn't just a problem with Gimp. It's a problem with Photoshop and basically every discipline where there's a bunch of file formats that have varying level

This isn't just a problem with Gimp. It's a problem with Photoshop and basically every discipline where there's a bunch of file formats that have varying levels of support for features. "Open" would then more correctly called "Import" for most file formats. If you want Open and Save to work with all file formats, you'd then need to restrict the UI to operations that work with the file format you have open. Otherwise, you lose data when saving. >> IMHO most people want to save in the format they started with and if they want to change it, something other than "save" is warranted. Most people when they save a file expect everything to be there when they open it later. That's only possible when you save using that applications proprietary file format.