I think the reason for this is if you are a novice user and pay the premium line to help you they will remotely connect to the hub and adjust settings for you. If the username and password is changed then they cannot do this. I maybe talking a load of copplers but im sure someone has told me this.
However if you dont class yourself as a novice user and are happy with your setup then change it.
Just to add only someone connected within your network would be able to get to the admin page anyway which requires the username and password. The main security is the wpa to stop people outside the network wirelessly connecting. If for instance this was in a shared house with tenants then you would definatly want to change it. If its your house with a couple of personal computers connected then there is no real point.
______________________________________________________________ **I am employed by Virgin Media** **Everything I post is in my own time and my own opinion**