You can either take the ticket, or tell them who was driving. You cannot say 'it wasn't me, but I won't tell you who it was'.
It is also a serious criminal offence to take speeding points on someone else's behalf (as it was suggested that government minister Chris Huhne asked his wife to)
In Sweden a clear photo of the driver is required for anyone to be fined.
As someone else touched on: in most states of Australia, the owner of the vehicle (as per the registration) is responsible. If you "don't know" who was driving your car it doesn't matter-you are responsible for the vehicle unless you have reported it stolen. Which I think is fair: if you're going to lend your car out, make sure you trust the person driving it.
In Egypt three speeding tickets means jail time (if I remember correctly), only not for the driver but for the owner. IMO that's just sick.
Sure, I could ask who was driving but I wouldn't know if they for some reason were lying.
And wait, what? Why should the owner care if the driver is insured? The vehicle is insured by the owner, as required by the law.
[1] Germany has Napoleon compliant highways while the UK was much more interested in resisting anything from Napoleon.