I tried a work around suggested by TrishGP on page one of this thread. She later posted that she was mistaken and it doesn't work, but it does for me! Export your document as a '09 version. I've tried it with Pages and Numbers, and they don't zip and are searchable. It's definitely still an issue – and a worrying move by Apple, if intentional – but hopefully this is a good enough hack for some of you.