HTMLtoRSS is a free Ruby based script for NetNewsWire which will, more or less, turn any web page into a new feed.
When ran, HTMLtoRSS checks to see if the page has changed. If it has, HTMLtoRSS makes a new feed entry with the page.
Installation: To use HTMLtoRSS, drop the script somewhere. Make sure that the script is executable. (`chmod +x html2rss.rb` from Terminal is one way to do this.) Then in NNW, select the File > New Special Subscription > Script... menu item. Pick the scipt. Then in the info panel for the script, set the script type to "Shell" and put the URL of the web page you want to track into the Args box. Repeat for as many pages as you want to monitor.