You can call them whatever you like. You donít have to like the answer.
This is the definition of Derby in sport - A 'derby' is a match between local rivals. i.e. teams that are from the same city or the same part of the country. These local games have a special place in the hearts of fans and players.
So, by definition your answer is incorrect - itís an opinion. Come down and experience the build up to a Cardiff v Swansea game and tell me itís not a Derby. Itís the same in rugby. The Blues v Ospreys is the fixture we look for first as itís our Derby. But please, as an outsider, continue to tell us what our Derby is or isnít.