When you really break it down, a roleplaying game is just a bunch of people saying stuff. It might be saying stuff about what's in your head. It might be saying stuff about what someone else just said. It might be saying stuff about the resting state of a platonic solid after ballistic motion followed by several elastic collisions with a level surface.
In the end, roleplaying is all just saying shit.
System is the procedures you're using to determine when you have to say shit, when would be a time to consider saying some shit, and what things can have shit said about them. There's a lot of wiggle space in there, because few to no systems cover all possible opportunities to open one's pie hole to embellish the evolving player[1. Where "player" includes the GM, of course.] dialogue.
Where system matters is in what it requires you to say.
Some systems make this requirement by simply demanding it: "When the roll comes up boxcars, tell the players that they've failed the Extended Contest. They should then roll a d7 against the So Your Character Is In Deep Shit table, and tell you the consequences they've suffered by the failure."
Some systems require you to say things simply because they need you to say something, otherwise the game is going to be really boring if you don't. "So Pat, the Astorian Enforcer levels its lasing appendage at you and demands to see your papers. What do you do?" Silence would be pretty lame right about now!
System vary a lot in what they demand you say, but they vary even more in what they need you to say but leave as an exercise to the reader to figure out.
We can compare games (ad hoc—this post isn't going to sprout a bunch of categories now) according to what they leave un-demanded that needs to be said. Two games might be similar in how they need the GM to tell the players what their dice rolls mean even after they know the number they've rolled. Other games make the meaning of the roll obvious, whether through the rules or through things that the game demanded the GM say before the roll.
And here we come to the inspiration for this post: I'm tired of needing to say certain kinds of things in games I GM. Partly this is because of shifting tastes on my part, partly because I just don't have time to develop (i.e., prep) all of the things that the game needs from me in order for it to leave the region of "suck" and have a hope of approaching the exalted realms of "awesome."