TIMSTRINGER Comparing Contribute to iWeb and RapidWeaver doesn't make any sense as they serve different purposes.
Contribute is designed to allow novice users to make routine changes and updates to websites (including existing ones). It's esssentially a scaled-down version of Dreamweaver that isolates less technical users from the complexities of HTML source, CSS, etc...
iWeb and RapidWeaver, however, are tools which allow websies to created from the ground up using supplied templates. Contribute does include some basic templates which can be used to create a website from scratch, but this is not the main selling feature of the application.
I hope this helps to clarify any confusion.
(Version 4.0)