Initially yes, and it is intended to be use only for clients, although not only from javascript, i.e. as the guide says also from flash, etc.
But nothing stops you from using it from the server too as it is technically possible, although I guess Google could stop responding requests coming always from same IP address, as would happen if you use your server instead of the client.
Yes, thats interesting... I wonder if they want to keep it quite (by making this info hard to find) or the developers of the API didn't think it through...