no, it's not a lie because the reader knows, by very definition of the genre, it's 'fantasy.' you're not trying to decieve anyone against their will. where's the lie? if i told you staring at the mona lisa caused cancer, you wouldn't believe me, eh? i hope not, at least. if that was my story and you *wanted* to believe for the sake of entertainment or whatever, you'd accept the 'lie' for as long as the story lasted. you certainly wouldn't start a crusade against the louvre.
fantasy and sci-fi are just a setting to explore a character or situation that exists in real life. if you wanted to excercise a theme, you could do it practically in any genre you want, right? if you've done your job well, the 'reality' is there despite what dressing you put on it. stripped of the fantasy or science, there's reality, wouldn't you say?
i don't think it's absolutely imperative that you know and the reader has to realize that, say, a dragon has a philosophic symbology in our culture (as it's got one in the eastern culture). so does a camaro or ripped jeans. it could help if you're trying to get a point across. if not, then it's just entertainment and you hope you get the right combination. if not, you wind up with 'willow,' if so, 'star wars,' which are pretty comparable movies in their basic elements, eh? or it's more likely i'm exhausted after a long day and have no clue what i'm rambling about.
is it really magick that's the issue? on the surface, perhaps. deeper, though, and you can supplant that dragon with a mustang GT convertible, orcs with corrupt cops, the wize wizard with grandpa and the ultimate evil with the CEO high in his corporate headquarters. with fantasy and sci-fi, certain things are fascillitated easier than others, but i wonder what 'spell' can't be accomplished in 'reality' given a fair exchange of objects and characters from fantasy to real life.
so, no, since fiction is a shared lie, there's no need to feel like you're cheating anyone. i guess 'magick' is a different symptom of the same disease, but it's a disease the patient pays to have. the option is to quite fantasy, turn your back on magick, and write fiction set in contempary times and dress your 'truths' in a different pair of panties until there comes a time to start questioning even the world in that genre, too. i mean, the landmarks and correct placement of mail boxes manhattan doesn't make the world any more real, just 'correct.' the reality exists in telling a story about humans, doesn't make a difference if they're hobbits, ghosts or robots, does it?