1. In some jurisdictions, the law authorizing the use of photo enforcement for speeding or red light violations specifically states that the ticket is issued to the owner of the vehicle regardless of who is driving. These violations involve only monetary fines and don't result in any points on the driver's license, so from a strictly legal standpoint it doesn't really matter to them who was driving.
2. By sending the response, the recipient of this summons has acknowledged that he received it. In a legal process where you want to keep all avenues open, this is probably one of the worst things you can do because it eliminates one potential line of defense (they mailed it to the wrong address, for example).
Check your Freep-mail in a few minutes.
In those cases what happens when the vehicle is a rental car?
The constitutionality of 1 has to be questioned. By their own admission, they are issuing the citation based on a vehicle, yet a vehicle cannot be held liable for a crime. Only a person can. And the person held liable must have some logical proximity to the commission of the crime; I might own the land where a murder is committed but that doesn’t make me liable for the murder.
Aside from its appeal as a revenue source, I can’t think these kinds of “owner pays” laws have any foundation to sustain them.