"Always On" option only there for Login

Hi just wanted to find out something.

So when your Internet connection requires a login (Example here http://i.imgur.com/DWOaJXF.png) you have the option to select "Always On" from "Dial on Demand", why does this option not appear when you DONT have a login, like on Cable, is it "Always On" already? 

I am asking because we have had BT (ADSL/VDSL) the whole time and we are about to move to Virgin Media (200Mbs/12Mbs) which is Cable and obviously I don't want the router always disconnecting or "Dialing on Demand"

Thanks