The point was most people in and around 10 miles of the sol, where the vast majority of fans are from, don't have a strong emotional connection with Boro. Simply because they don't interact with Boro fans, so they aren't getting the piss ripped at school/college/work etc if they lose. In this area there is no day to day banter between Sunderland/Boro fans. As a result of this there is no strong dislike that you would normally associate with a derby match.
It's acknowledged Old timers like yourself will have strong feelings against Boro because of the fierce battles you describe off the pitch in the 80s.
Sunderland fans who live in the very south of Durham/teesside are naturally more likely to dislike Boro also, because they will have regular interactions with Boro fans. This raises the stakes of the fixture. There is "bragging rights" to be had in Peterlee or Billingham that aren't in Southwick or Shiney Row. So when you keep asking me about the 10 mile thing, this is why, because I acknowledge it's different further south.
Some fans feel it should be labelled a derby simply because of the distance, regardless of the lack of emotion for the majority of fans in the fixture.
So in a nutshell going through this thread, to some its a derby, to some it isn't. It depends on what criteria you use.