I suspect this is the case:
http://myhompage is a Web Application, with a site Collection in the
root (/). This root site collection is an explicit managed path.
The 'sites' you mention, are actually 'site collections'. A Site
Collection cannot span content databases; it must exist in a single
content database. A content database can host any number of Site
Collections. You can backup at the Farm, Web App, content DB, or Site
collection levels.
If you don't already have one, you might want to read the Disaster
Recovery, site collection, content database, and Web application
sections of the Microsoft Press SharePoint books.