It's not the ideal solution, (you would need a bot spidering the sites in question and looking for updates* - I am not aware of any free services which would provide this service, but there may be paid ones) but you could use Google Alerts to alert on an exact phrase which appears in the site template for each of the sites.
(* Disappointingly, Google's
site: operator is not available within Google Alerts)
- Sign in to your Google account (Gmail) and go to the Google Alerts page
- Enter the exact phrase
"Pro Webmasters Stack Exchange" (with quotation marks) in the textbox at the top of the page
- Type: Everything
- How often: As-it-happens (or your preference)
- Volume: All results
- Deliver to: Feed
This configuration would compile a feed (stored in Google Reader) with the results which Google picks up (though not necessarily any publicly-available change).
Edit: I have not tested it, but it appears as though creating the alerts as feed items (which, by the way, you will need to add to folders using the Manage Subscriptions dialog in Google Reader in order to see) will also create a publicly-accessible Atom feed which could be monitored from any other syndicated feed reader (which may be particularly useful if you are automating your solution - you could programmatically filter out results from domains other than those you wish to monitor).