It is...the fans dislike each other with knobs on!

I believe the late lamented Bazza was a Sharks fans and he always referred to St George as St Choke...

The Sharkies really don't like the Dragons

maybe some of the amalgamating and clubs dropping out of the main league is why you dont have the same level of passion as english derbies,even with your better attendances.
i have read that newtown fans were quiet partisan vs other sidney teams

Everyone loves the Bluebags (Newtown) nowadays. The same can't be said about Souffs anymore

If you go to the lower league games
Wests(mind you West hate everyone) vs Balmain they hate each other
Illawarra vs St George (in the juniors have had games where Craig Young has had to go onto the field and tell both sets of teams to settle down)

When I was at the Bears and we made the Premier League Grand Final in 07, it was amazing to see how many people had a soft spot for Norths with people often referring to them as their "second favourite team"