The more you play you'll find there is a big difference between true skill and pseudo skill on many machines.
For example, many old machines could have all their money emptied out of them by players who were good enough to hit skill stops constantly, and the developer hadn't thought this would be possible.
However, play any Betcom machine you find in the downloads section and you'll find things like the very top reel that you get to spin after the 'deal or no deal' type feature is 'pseudo skill'. In other words, you're supposed to think if you're good enough you can stop it on mega streak, but in reality it stops where it wants and your input is irrelevant.