In WebSite Watcher, this has been discussed extensively in the past.http://www.aignes.co.../viewtopic.php?t=780
Last comment was "But an optional word-by-word comparison is planned for a higher version." but the developper seems concerned with performance. To my knowledge, this still remains to be implemented. WebSite Watcher may be "one of the most respected apps in this category", it still does not perfom word-to-word comparison, unlike other software.
Anyway, the main reason that made me switch is the below-par RSS reading feature.
Concerning the legal situation of html scrapping done by Openkapow, I guess that it depends what you do with it. If you scrap protected content, publish it, and make it widely available, without the consent of the content owner, you may run into trouble. But if you use it for your own purpose only and keep the URL generated by Openkapow for yourself, then I don't see any reason why it should not be OK.
Furthermore, you should not publish passwords inside Openkapow robots. Logins / passwords must be passed as arguments when calling the url, so accessing a password - protected database still requires to know the passwords - therefore I do not see any legal problem. This is just a tool.
You may have a look at Openkapow forums where this question should be discussed.
Although the big talk of the moment is APIs and mashups, I bet that web scrapping / html scrapping is the next big thing. This is my 1 cent!