The official Motor City Online site from EA features a last goodbye message.. Here is the full message:

We at Electronic Arts and MCO Staff both past and present would like to say thank you for being a part of a great online racing game experience. Motor City Online service ends today, but it will live on forever in the hearts of the racers who loved the game.

Thank you for all your enthusiasm for Motor City Online and making it such a great place to play.

Regards,
MCO Staff