The pages hierarchy is very useful, however it doesn't take into domains and subdomains into account.
If a piwik website tracks multiple domains or subdomains it'd be very useful to build the pages hierarchy by first matching common domains, then common subdomains, and then the path.
In our case, we're allowing users to create new groups which are reflected as subdomains. All groups have the same path structure, but completly separate content, so it doesn't make sense for us to only group them by path.
I understand this might not be desirable for those who have the same content on multiple subdomains (say with and without www), so a flag whether to include (sub-)domains in the hierarchy might be desirable.
Please see: http://piwik.org/faq/new-to-piwik/faq_104/
If you track many subdomains in the same Piwik website, you might want to see the domain name directly in your Page Title reports. If you want to show support.example.org/Homepage instead of simply Homepage, check out the JS setDocumentTitle documentation