Why would Toyota be able to get at this data without physical access? Doesn't look like there's evidence of radio capability, unless I'm missing something...
You don't think other companies are capable of slipping a GPS/3G chip in your vehicle to do the same thing? I don't know what the legality of this would be, but I'm sure they could slide a clause into the pile of documents you sign when buying a car.
The difference with a GM vehicle is that the customer knows the data is being recorded.
I'm not sure what documents from the manufacturer (and consequently the operator of the GPS hardware/database) you're thinking would need to be signed, but the only stuff I signed when I bought my car was from the dealership and the bank.