Is there always exactly only ONE home network ?

The short answer is no, that is not true.

Windows 7 let's you select a network location (type) for every wireless network connection when it is used first time. This location can also be changed later.

Think it as an added layer of security. Home and Work networks are quite safe because you know the other users / computers on that network, whereas Public network is suitable to use when you are using a WiFi connection on an airport, café, hotel etc. where users / computers you do not know can join the same network. Public network is therefore more closed, making it more difficult for others to access your computer.

At the moment for instance I have 4 networks set as Home network, the two places I am living in, my office and my mother's house back in Finland. In these four places I know other users and computers, and can trust that no harm is done to my computer by others using the same networks.

Kari