Some of these machines (at least in europe) are actually required by law to average out to a certain return percentage over a set number of bets.
This means they need to compensate for naturally accuring bad streaks. (And good...)
You wouldn't see that in most US jurisdictions that have proper gaming laws and review (NV and NJ being the big ones).
The software and underlying math is audited by a third party and verified to produce the desired average result over millions of plays, but cannot adjust the odds dynamically to make sure that percentage is hit.
