Why? If your players joined your game believing that their decisions actually matter to the outcome of play isn't it disrespectful to ignore them and just do whatever?
The DMs authority only exists as long as there are players at the table. No players, no DM and thus no authority.
Why would players want to play in such a game? As a player, what is the appeal of such a game for you?
If you treat people with respect and do not lie to them constantly, there will be fewer walk outs.
IMHO it is only cheating if the players are unaware of it. If a DM advertises a story focused game and claims that things will be nudged here and there to maintain continuity, and players join the campaign under this premise, then no it isn't cheating. If the DM offers a fair game then constantly fudges then it IS cheating. It is cheating because of the breach of trust in this case.
Okay, you're asking me several questions. Let me see if I can respond to them all.
First of all, I have never seen a DM do so much fudging that a player's choices didn't mean anything. Quite the contrary, as a matter of fact. The DM's who fudge the most, tend to be focused in their style on tailoring the game and its challenges to the players' decisions. They will adjust the encounters, hit points, dice rolls, and even the rules they are accustomed to using, to give the players the kind of experience they want. I suggest you read what I wrote to Celtavian above, in post #357, because what's actually involved in a relatively small amount of fudging is nowhere near disruptive enough to stop you from making an impact with your decisions in play. Maybe you would feel cheated out of the chance to face the monsters as you expect, but those expectations are not the standard based on the rules, in fact. No DM wants you to feel like your character's decisions don't matter, and however they fudge something, I am sure they have your best interests in mind.
Now, the next question you ask is actually a statement. Again, as I just told Celtavian, the rules actually say the DM should change any rules he wants. You may feel cheated out of the experience you expect, but that is a non-standard experience which the rules do not make any effort to guarantee. The DM is authorized to do anything by the rules. I have heard it called Rule 0.
Now, a question. Why would anyone want to play such a game. Well, it didn't stop Mr. Gygax from making the game this way so maybe you should think about that. Mr. Gygax told the DM first to change or ignore any rule. From where I am standing, it looks like the game was pretty popular.
Now, you say if I treat people with respect and not lie to them "constantly" there will be fewer walkouts. The DM does not disrespect anyone by playing D&D. No, sir. The DM does not lie "constantly", either, whether he or she is using the rules in one way or another. The players are not entitled to any explanations or updates about any modifications the DM makes, let alone consultations and veto authority over the DM. As a player, you are supposed to treat the DM with respect and permit him to make any modifications he wants without informing or consulting you. You deserve to know as much about the rules as the DM permits you to, and it is according to his preferences what that will be.
Let's look a little deeper into this claim about dishonesty. I was told a player would leave if he learned I fudged the hit points, not that he just wanted to know if I did. I am sure the player could enjoy the game for years without ever knowing fudging was ever done, and I doubt very much he would say he wished he opted out because since fudging was done, the game wasn't run as he expected it to be. If the player is having a lot of fun, why spoil it for him and tell him to leave because you want to do it different? You could tell them, perhaps if he requested the information nicely, but this is beyond the scope of what the players need to know. The other players' enjoyment could suffer from telling them, even if they are okay with it. Just take my word for it.
Your last comment talks about a story focused game. I know many story focused games which didn't do much fudging, first let me say. You mention a breach of trust. If your DM agreed to run the game as you expect, and then didn't, sure, that would be a breach of trust and dishonest. But the standard way to play the game, and to run "a fair game", is to invite all the fudging the DM wants. That is according to the rules.