Benedict has known Una Stubbs (Mrs. Hudson) his entire life because she is a close friend of his mother. So the affection Sherlock shows Mrs. H is completely real and completely Benedict's doing (Moffat didn't write it in the script initially).
18 months between seasons of 3 episodes. Don't talk to me about waiting a week, silly one.<<<sometimes it's more than 18 months. And we have to come up with theories to the cliffhangers at the end of every season just to survive the wait