Yes, I would mention that the suspension for those with the 18's is different and there is no way the factory would just substitute them for the 19's. I also have a hard time believing that they would just change your order and give you a vehicle with 18's when you wanted the 19's.
Given the date (2 days from the end of the month), I wonder if they found one matching everything else you had and it just had 18"s? Have you double checked that every other option is as you wished?
I cannot believe the factory would change that without the dealer. I wonder if the dealer was just told that they would notbe able to get one with 19"s and the dealer went ahead and changed it. He knows that if you don't take this one, he will find another buyer fairly quickly.
I think the dealer messed up your order - Have you seen the sticker on the window, does it mention the 19"s and then substitution for the 18" wheels and an allowance for the difference. I would think the window stickers are made up first for that particular order than follows the vehicle through assembly. I cannot imagine them just making this substitution on all orders for 19's without contacting the dealers/customers. If it is not what you want do not accept delivery!
I would have to agree that the dealer probably messed up but I would see if you could test drive a vehicle with the 18" wheels. From what I read (I also have 18" wheels on mine) the 19" wheels have a rougher ride because the sidewall profile is lower than on the 18's. I think that the ride with the 18's is really nice and that you might like them over the bigger wheels.