First off, Maul really did use the Force... notice how prior to Episode I, a lot of fans had this thing about assuming you actually couldn't use "offensive force" during a saber duel, because it required too much concentration or something (at least not against someone who was "well trained").
Maul broke this, using not only the typical "jump," he actually Force pushed Obi-Wan off a ledge while in a saber lock! He also casually used a battle droid part to open a door while fighting two Jedi at once. It's quite clear that whatever this might have been in the original films, it's no limitation on Prequel era Jedi/Sith. Maul has plenty of control over the Force.
Maul isn't the "only a swordsman" guy (did you also notice how he used physical blows like kicks during battle?). For that, you want General Grievous (whose "Jedi arts training" clearly only encompassed fighting, because he had zero defense against a simple push Episode III).
Second, I know that "having hands made of flesh" is something that is offered as an explanation in the Expanded Universe as to why VADER never uses lightning, but it isn't a very satisfying explanation for me. None of the other force powers seem to require physical hands to perform (even the movie "gestures" appear to be a tool of focuser for the user, not strictly required to do something). Couldn't he just channel it through his "stumps"? Why not make the robot limbs out of some material that could safely channel the lightning if that was the issue? (the Prequels demonstrate that this technology exists in the Star Wars universe, and we have no proof that "sith" lightning is really anymore dangerous than any other form of electricity they routinely handle).
The real reason is that Lucas hadn't thought of "Force Lightning" until he started working on Return of the Jedi. By then it could have been chalked up as some kind of mysterious "ultimate power" that only the Emperor knew. Episode II changed all that (well, and the EU for years has basically had every schmo who has been around using it, as mentioned... maybe the "Secret" got out of the bag after the battle of Endor?).
It's really never explained why some can use lightning but others cannot, except the outside the movie "well he didn't have arms so..." which is silly, because we can then ask "so why didn't he get cloned arms so he could throw lightning, if it was so important"?
Then the excuses because sillier.. "he forgot," "too sad," "Palpatine wouldn't let him but he never took it as a slight against him,"
If it was "Palpatine was deliberately holding him back" that's silly because the whole reason Palpatine supposedly switched to Anakin was because he wanted that power and potential for himself. If he had no problem giving Dooku "the secret" (assuming it was) why not Anakin?
And I don't buy the "clone body parts don't have the force" because while this is an EU thing, it's totally at odds with the Episode II novelization. Plus, part of the logic of the Clone troopers is that Force users have influence over them (otherwise what are we supposed to assume, that anyone barking an order at them would gain their loyalty? The Separatists should have used big loudspeakers on the battlefield to countermand them!).
It's just a movie inconsistency, sort of like "Sith Eyes."
PS: Anakin uses lightning in the "Episode III: Revenge of the Sith" game too (so I guess in the game's anything goes, but someone who bought into the "official excuse" could argue that he only uses his left hand for that, which is still organic).