I would say it may be common but I wouldn't say it's necessarily the norm. I think it depends on the personalities of the A and the partner. We've done it multiple ways. We've had separate individual accounts, one joint account, and most recently separate joint accounts used for different things. He's been in control of the major finances for the last 10 years. Prior to that, I was in charge. My sister's AH is in control of their finances and she doesn't even have access to the account. My parents have always had separate joint accounts and my father's been in control of/responsible for the finances for the most part.
I'm looking forward to having total control of the finances again when AH moves out this weekend. I think this is one of the most difficult areas in a relationship because we all have different investing and spending views.