It's all about being paid the going rate. Potter has kept Brighton up 2 years in a row. By virtue of that he has helped earn the Club Millions. Why shouldn't he get paid the same going rate as other PL Managers ?
Potter came to Brighton with no PL credentials, so I understand why the Club tied him to a long contract on a very low rate but he has proven himself a capable Manager in the last 2 years. So if Brighton want to keep him then they need to match what others would potentially offer him.
Maybe its not all about the money.
GP wont stay forever but he wont leave because of money and it wont be for Newcastle.