Why do pet shelters lie about the breeds of their dogs?

[Crony]

The love of my life is my 1 year old (this month) puppy. I got him form a shelter when he was 2 months old and I was told that he and his brother had a purebred Rotty mom and they weren't sure what the dad was. He was too little to tell really what breed he looked like (he only had Rotty coloring), but it didn't matter. Well almost a year later he is skinny, has an extra long nose and is extremely well tempered. Their is not a drop of Rotty resemblance. He has a Dobie body (dropped chest and tiny waist) and a German Shepherd neck(fat), face, tail and ears. He also has a German shepherd temperament and smarts. He is completely black with brown Dobie markings, except for one tiny white dot on his chest. Everywhere we take him people ask if he is a Dobie, and/or German Shepherd. Why would the shelter lie and tell us that they also rescued his Rotty mom? Their is No Rotty in him at all. I wish I could show a pic, but I don't know how.