Cruise control on flat road at 65 mph ...
Zero the average speed display by pressing Enter ... After about 10 seconds it shows 62 mph
The error remains a constant 3 mph after extended driving ...
Can the dealer correct this discrepancy?

Also how accurate is the speedometer? ... everyone seems to pass us at 65 mph onthe highway by about 5-10 mph faster.

2013 with 1250 miles and original 18" tires

 

A lot of factors to consider, like the kind of tires and tire pressure you have.
+/- 2 points seems to be norm.
Im basing that on speedometer vs a cop's radar gun.

on your SECOND question, nothing to do with the speedometer but with the OTHER drivers.
That seems to be the attitude here in the US,
There seems to be an unwritten rule where you can go over the speed limit as long as it's not over 10mph on a free way or more than 5 mph on the side street, like your subdivision.

Here in LA posted speed limit is 70 and most people are doing 80.
CHP ( state police) will stop you if they clock you At 85.

 

I wouldn't worry about the average speed ... the statistic really isn't good for much and is just a general number to give you some idea about your general usage of the car. Relative to other drivers passing you by 5 to 10 MPH, that is just the way it is when you drive the speed limit. They are exceeding the speed limit. The easiest ways to check your speed is to: 1) use the mile markers (if they exist) on your local freeway and an accurate watch; 2) get a second opinion from a standalone GPS system reporting speed. These two methods can be compared to the readings in your car.

 

I agree. Avg speed display is a broad average -- not scientifically accurate to the nth decimal position that would be prohibitive in cost to produce for a consumer product. I don't expect any of these sort of calculations on my vehicle to be 100% accurate, including the "minute-by-minute display" I have on my RXh showing MPG and energy production in the last 60 secs. I've had multiple Lexi, as well as my BMW 335i that could present a number of calculations like this -- but always took them as just an estimated data point. The only couple of displays like this I really care about being fairly accurate is odometer and speedometer.

I also agree about people passing -- here in CA, it's the modus operandi of a lot of drivers to pass anyone -- including those going at the speed limit. While I have just turned 800 miles on my 2013 RXh, using road markers a few weeks ago, I was satisfied that my speedo was within reason on both the dash display (analog) and HUD (digital). Honestly, when I rule out the few drivers that like to pass for passing sake, I am confident all is well with the calculations being presented in my 2013 RXh on 19" wheels.