"Lightroom employs a database to store the changes. Lose this (or the computer), and you'd be hard-pressed to recover anything."
No. For DNG, TIFF, PSD and JPG files the metadata is written into the original image file. For proprietary formats such as Pentax PEF files it writes the metadata to XMP sidecar files stored in the same folder as the image file.
I can create a new catalog and import a folder full of files I've already processed and Lightroom picks up the editing work already done and the keywords assigned, from the image files or from the sidecar files. The editing history isn't there, but the preview image displayed shows the result of the edits that were made previously, and of course if I hit the "reset" button I have the original unedited raw image that came from the camera. I think the Lightroom catalog (the .lrcat file and associated folders) holds the preview images and the editing history. As long as I have the image files backed up in their folder structure, I can create a new LR catalog with a fresh installation of LR.