Where does Siri acquire it's list of recognized locations from?
The Reminders application does something similar, it knows three locations: Home, Work, and Other. When you assign a location to a reminder, you are presented with the current location, those 3 previously mentioned locations, and a "Choose Address" option. The 3 locations are taken from the address book's contact information for yourself. The contact that represents yourself is determined by the setting under Settings > Safari > AutoFill > My Info.

I'm guessing that Siri uses the same My Info setting to determine locations such as Home.

Note that the name of a contact has no effect on the Reminders app. Even if you have a contact named "Home" it will not present this as a default address unless the contact is also assigned to the My Info setting.

Update: Siri has its own My Info setting which is the exact same one accessed in Safari (i.e. they always have the same value).