Hi,
Quote:
the width of the content area of a page with sidebar is 730px, right?
Width of Content area with/without sidebar is 730px
Quote:
What´s the width of a page without sidebar?
Answer is little tricky 
Here are two cases.
1. When there is no widget in the sidebar. It means, you are not using sidebar and the content width will remain the same i.e. 730px. Theme will adjust the content layout automatially.
2. When you use Full Width, No Sidebar template. It means, you want to use full width. In this case, content width will be 1110px
Example of Full Width: http://themes.designorbital.com/arcane/full-width-no-sidebar/
Thanks