There are actually places in the US where the speed limit is 80 and 85. That's not 100, but it's quite a bit more than 65.

I was not aware. I make the same case with 85 as I did 65. Throw in a GPS and you could make the distinction.

Then in 10 years, someone, somewhere decides that 90 is acceptable on a specific road. Now all cars with limiters need to be modified. Want to be able to change it remotely? Now you add an attack vector. Throw in a GPS? Now you're asking for additional government monitoring that is mandatory and might be (will be) used for spying purposes.

You could design a GPS speed limiter that doesn't track location, TomTom's had an "overspeed" warning 10 years ago, it would go orange if you went over the speed limit and go red and make a bong noise if you went way over, My old boss used to drive fast so I saw that quite a lot (in the end I told him I wouldn't share a car with him if he didn't stick to the speed limit).

Nissan GT-R's have (at least in Japan, where it is as far as I know mandatory, not sure if they are removed in international sales) limiters that deactivate when they are on a white-listed race track.

They do that in Germany. Higher end cars come with a governor that caps the speed at 250 km/h. (That's around 155 mph, for the unenlightened.)

That's still below the legal speed limit on some German roads. But it's above the highest recommended speed of 130 km/h (~ 80 mph).

The governor is merely a gentlemen's agreement between the big car manufacturers, and any garage will take it out no questions asked.

You may actually need to go 100 MPH in traffic. Speed limits are 85 in places, and 15 over that may be required to maneuver.

Speed limits on interstate class roads seem pretty dangerous to me - you can watch people thinking "but I'll get a ticket" and backing off at bad times. Of course, I guess of there were no signs with numbers on them they'd drive 115 and kill themselves.

Because fines provide revenue?

Speed limit on the highway by my house is 70. If you are doing less than 75 during rush hour you will be passed by a stream of cars. I've been overtaken while doing close to 90.

Large sport bikes have governors. Want to guess the limit? 186 mph.