The directly download URL trick works for native Google documents as well. This comes really handy if you want to give users an option to download your Google Document as a read-only PDF file or your Google Spreadsheet as an Excel XLS file.
Any document in your Google Drive has a URL like:
https://docs.google.com/document/d/DOC_FILE_ID/edit
Replace /edit with /export?format=, add the file format that the document should be saved as and your download link is ready (example).
https://docs.google.com/document/d/DOC_FILE_ID/export?format=pdf
https://docs.google.com/document/d/DOC_FILE_ID/export?format=doc
The above links will now download the same Google document in Word (.docx) and PDF formats. You can also specify txt, html, odt (OpenDocument) or epub for downloading the Google Document as an e-book.