See, that's the thing: you've been gaming with the same people, and they have a deep abiding trust that you'll deal with it.
In a crunchy game, especially one like 4E or D20, a player MUST know the rules in order to play effectively, if only the rules for their own abilities.
It actually reinforces the need for players to know the rules as a generality, while also pointing out that, for some groups and for some gamers, it's not needed.
My WFRP (1E) game, I have a new-to-WFRP player playing a wizard (started as a Wizard's apprentice). Experienced gamer. All I had to tell him was the basics of combat: On your initiative, you get your action, and you roll d% for either adjusted WS or less to hit with melee, or adjusted BS or less for ranged; or you roll 2d6 for current magic points or less to cast. If you go faster than walk, you can't attack nor cast; exception: if you charge, you have to move at least 4yd straight at them, and get a +10WS and +1 Damage. Damage is 1d6+(your S) -(target's T)-(armor in location hit), and comes off wounds; at the end of the round, if you are negative, you're back to zero, and if a hit drives you neg, you take a crit. Called shots are -20...
That gave him enough to understand that he's not likely to hit if he does fancy stuff, that he can and should charge, and that he's not as fragile as 5W really looks. (He's 2T, so he IS fragile, but we didn't tell him that.) Since everything else works similarly in WFRP, it was enough. When he got XP, we taught him to use them.
For CT, the combat system is straightforward, but table driven. I hated it until I cornered my Ref, and got him to explain it. Then I found it workable, becuase I now had a clue about what weapons were useful and to what ranges. He used a "2d6+Skill" for announced target number or more as his normal task mode. To try unskilled, 3d6 for Stat+JoT or less.