Not sure I'd say they cheat just because they have a top score.  The individual records are suspect though.  I made it through not quite 20 matches (Cth or Dth round) and was closing in on 1.6 million.  Got to the point where I was Hoping I would not qualify.    But, I'm not good enough (or don't use turbo) to get the top scores in the individual matches, but can consistently qualify in each event.  I can get around 4 lives saved up, but as I'm just good enough to squeak buy in some events, I eventually tire out and don't qualify.  But, I could see with patience, and a lot of time on my hands, those top overall scores are reachable without cheating.