granted, he wasn't headmaster when he went to get tom, but still. doesn't it seem like harry would have rated a visit from dumbledore himself? it's not like people would have been jealous of the personal visit or something... i mean... its harry potter. anyway... just a thought.
also i think hagrid just hada greater dramatic impact as a messenger from the magical world. DD although obviously magical isn't quite so obtuse. hagrid however is, and made the news that harry was a wizard more of a shock to the system. dramatic license that's all it is. 