hmmmm....my 2 cents. I currently have a 2 lb, 1 lb 12 ounce and a 1 1/2 lb yorkies. I AM more careful with them. I watch them more closely around my children. I watch them more closely around my other 2 yorkies...but then again, I'm talking about puppies.
But, I would treat an adult 2 lb yorkie the same. They're going to be smaller in size, have smaller frames so why wouldn't I treat them differently?