they always indicate tire wear on a 1-10 scale with your service summary... at least thats what they do at my dealer... so if they have been reporting that on the service summary... then it'll be on you for not paying attention. Although i do agree that should give a verbal warning about any problems, especially saftey related like tires/brakes.
Since you are forced to get new tires, just look into the after market (tirerack.com or your local tireshop), the tires at the dealer are marked up as you probably know...
i reccomend
http://toyotires.com/tire/pattern/versado-lx ill be getting these begining of next year, itll be my second set
