I don't know of many dogs with this wonderful quality, but I don't think it is anything to worry about. Both my Yorkies, Peanut and Prissy are SO YAPPY! However, my sister has a Yorkie and she is super quiet.
Between the 3 Yorkies, all of their little personalities are so different.
Peanut is older so he is more laid back, set in his ways, a little grouchy, grumpy at times, touchy, stubborn and acts like an old man. Prissy is bouncy, hyper, playful, friendly to everybody she meets, hard headed, determined to get her way, very protective and a spoiled brat. Jasmine, which is my sister's dog is so quiet, calm and mellow. She only barks if someone rings the doorbell and even then it is just a very muted bark. Must be nice! Mine bark and growl at every little thing they hear. They are definitely good guard dogs I guess. ;-)
