It doesn't really exist?!
It's an official ceremonial county. It very much does exist.
I have a few friends from Oldham who class themselves as Manchester. Greater Manchester is not Manchester, but you could say you are from Manchester as an abbreviation of Greater Manchester very easily.
Your other example, St Helens isn't in Liverpool in any way. Merseyside is not Liverpool. Merseyside is another ceremonial county. To say Merseyside and Liverpool are the same place is completely incorrect.
Leigh is a part of the Wigan Metropolitan Borough. It's not a part of Wigan (the town) but is a part of Wigan (the borough).
Are you trying to tell me there are no Wigan supporters in Leigh? If so, you're speaking rubbish. Just because you're from Leigh doesn't mean you automatically have to support Leigh. You don't pop out with a Centurions shirt on at birth. People can have links to wherever they like in whichever way they feel. There are tonnes of people in Leigh that class themselves as from Wigan. It's only because of the RL rivalry that certain people won't class themselves as it.
The thread isn't about Dream Super Leagues in the slightest. That's called "thread drift" and it deflects from the actual topic discussion. It's just good forum practice, fella.
Well someone is grumpy.
It doesn't exist. It was an invention for government. Manchester is not an abbreviation of Greater Manchester. Peope from Oldham who say they are from Manchester probably grew up gong to Manc alot. No one from Wigan would say there from Manchester.
If Wigan is in Manchester, then St Helens is in Liverpool. Neither are from Neither. People will only say they are from the city when talking to people who don't know about places as its easier to locate Manchester or Liverpool on a map.
As for the hissy fit about supporters being from Leigh etc. Where did i say they must support Leigh? Stop making up rubbish. I said that taking the population of the borough to measure potential support is silly as just because technically you live in the borough of somewhere doesn't mean you have any connection to the town.