If they are manipulating how often a Royal Flush comes up, then they are CHEATING. There is a big difference between adjusting the slot payout percentage and manipulating how often a win occurs on a game that is supposed to be random (e.g. anything other than slots).
On slots, they 'weight' the symbols that show on the reels to adjust the payout percentages to suit their pleasure. In a nutshell, if there are various symbols on each reel (blank, cherry, bar, wild/multiplier, 7, etc), they will give the ones that are worthless (blank) a higher 'weight' than the good ones. That means that you'll hit the worthless symbols more often than any others. Depending on how much 'weight' you apply to the symbols, the payout will vary accordingly.
This obviously cannot happen in a game that is supposed to be random (like roulette, craps,
bj, videopoker, etc) since the odds on the winning combinations in those games are mathematically fixed (like getting dealt a pair in a 5 card hand from a 52 card deck is about one in every 4 hands). Any manipulation of the random outcome on these games would be cheating.