You aren't the only one with this experience. In the early 70's, I knew a family - lived around the block - and we had a big block party one time; I was looking for the one son who was a couple of years older than me. His old Chevy van was parked in a drive on my street and I was told to look for him in there. I knocked and when the van door opened, there he was tokin' on a joint with a couple of other potheads and HIS MOTHER. She was smokin' the weed right with them. I thought she was disgusting and was glad I had a good mom.
Not much has changed, many people still smoke marijuana, I am 21 and know many of my friends parents smoke on a regualr basis. Even people who you would never think would smoke do, like your doctor or lawyer.