Ok this is strange, the <!--more--> and the_content() are not working as expected in the live installation, while the development copy running on my machine it does.
In particular, in the live installation when rendering the single article page, only the preview text and the "read more" link are shown, while instead the full article should have been shown.
I really don't know what to try. The hosting is s*rvage, other wp installations are always been ok there. I tried to deactivate all plugins but still, the development installation with all the plugins works as expected. WordPress version is the same 3.3.2. PHP is 5.2+ on the live, 5.3 on my machine.
The trick the purchased theme uses to show the full article is
global $more; if ( !is_single() ) $more = 0;