Plugin Version Numbers

Is there any reason why a plugin’s version number would not always be the same as the version of wordpress it was tested up to? The version numbers mean nothing to most users. The only number that really means anything to them is which version of wordpress the plugin has been tested up to. So why not just make that the version number for the plugin? But this would mean the first version of my newest plugin would be 3.3.1. There would never be a version 1 or 2. Is there any wordpress convention that says plugin developers are not supposed to version their plugins in that way? I couldn’t find anything about this in the documentation.