I think that another thing is that the very small yorkies (under 3 lbs full grown) are often that small due to a serious medical condition. So when you look at the statistics, you would see a decrease in the life span when you factor this in. Obviously this isn't always the case, some are very healthy.
Lily is around 1.5 - 2.0 lbs. She is small due to hydrocephalus and MVD. She will not have a long life but it will be a happy one
