@sarahchager: I think you're talking about two different things. InDesign is a layout tool — it's designed to let you lay objects on a page (whether it's a print or interactive page, setting the relationships between objects, and making it all look pretty). Exporting to EPUB, SWF, PDF, or print is one thing. Exporting to XML is very different. The fundamental concept of XML is that is breaks content and form into two different things.
What you're wanting is for InDesign to be a page-layout tool, an XML editor, and an XML database (a place to hold all the XML content so that you can do stuff with it, such as give it different forms, export it, etc.). I don't argue with you that this would be cool, but that's not what InDesign IS. InDesign works best when you drop stuff into it, make it look pretty, and output to some format that people will see (print, pdf, swf, epub).
There is no doubt that you can tag your content in InDesign, export it as XML, and then re-use that for Web, etc. I'm just saying InDesign isn't well designed for that.
Will it be someday? I hope so! But I'm not holding my breath.