That isn't true mate, Of cours they have to report the amount of tickets sold for tax reasons etc. But some clubs Spurs for example report the actual matchday attendance the likes of Arsenal and West Ham United for examples use tickets sold as their official matchday attendance figures which scews the facts.
At various times over time both West Ham and Arsenal have had multiple attendances in the mid 40ks but they report the tickets sold as their official attendance so they are both being economical with the truth and most other clubs do exactly the same by the way.
Maybe because their fans are deluded and have big mouths, Sunderland clearly have a better history than Leeds United and Sunderland are ahead in all time average attendance table.
With no disrespect intended Sunderland is a financially challenged area compared to Leeds and that has a big impact on matchday attendances, Why don't these gobby Leeds fans compare their ticket prices and attendances to London clubs.
The fact that one of them hideously states that Leeds United have a top 5 or 6 fan base in the country

says absolutely everything about many of them, they would just make the top 10 so deluded and clueless.