Tires showing metal treads

i purchased a 09 Cts V ,which now has 22000miles , i have had it at crest for couple recalls from manufactor and also regular service , i recently had my cts-V serviced in my home town which is hour away from nashville m and the GM cerified Tech, told me the tires were worn out on the edge due to inproper alignment and had to have been going bad with no more milage that that was on them . guess because they are higher priced ,"quote"'service man @crest Performance soft tires , they wear out faster . .my wife drives this care with my Grandcldren in there so dounbt there aws much performance driving going on /, I called service dept @ creat and they told me , Cadilliac Recommends alignment every 15,000minles , First time i ever heard of this , and i have several Cadilliac , escalade , and also a XLR .This is my second XlR, and also had DHS and deville from Crest over trhe years My service manager thought Cadilliac should or would have taken care of this problem , The service guy at the counter of Creat cadilliac stated that is was'n Cadilliac problem . May Have to Consider another alternative when purching other vehicles ,wow cant believe that kinda business would be that way . Sincely Dorris L.Lamb.