Here's an automator workflow you can use:
RemoveAndOptimizeWdgtDefaultImages.workflow.zip (104.9 KB)
It prompts for files; you can select multiple .wdgt documents. It then deletes the Default@2x.png and runs the Default.png in ImageOptim (it must be installed to work).
This is correct to my most recent knowledge; we saw it documented and added support. I went to test and was thrown for a loop when it wasn't used! I kept it in thinking at some point they'd use it, but I suppose they may never do so now.
Definitely something we'd like to do!