I.. Really don't see how having house rules and fudging dice rolls can be set as equals here. Well sure, you can have an house rule that you'll fudge rolls, but now that's just being silly, really.
Having an house rule in a game of Solitaire is saying "I'll stop after going to the pack three times, and go three cards at a time", as opposed to going through the pack as many times as you can. Both are accepted forms of playing solitaire. Fire the came up on your computer, you'll see. Fudging, (to me), is like going through the pack looking for the card you want, and pulling it out.
The best "proof" it's cheating is to ask yourself "what would I think if a -player- fudged a roll?" It could very well be because he thinks it would be more dramatic to have a crit against the dragon right now. But I doubt many of you would think it's a good idea to let the players fudge the rolls. Why not? They should have a say as to how dramatic the game is, shouldn't they? So why is it ok for the DM to do it?
I'll let you in on a little secret. I fudge monster HPs in pretty much every campaign I run. And sometimes, I even fudge die rolls! Aha, I lied!.
Well not really. I only do so in the first couple game sessions of each campaign. Because I'm not that good at looking at my PCs sheets, and figuring out just how tough they are compared to the average group, and as mentioned, CR is iffy at best. Could they take 12 goblins, or would 8 be all they can realistically take? I dunno. But after running a couple of sessions, I -do- know. And then I set things up at the level of deadliness I want it to be. And -after- that, no more fudging, because I set things up right from the start. Still, yeah, I can have a night that I roll very well, and my players roll crappily. Or, the reverse, and my BBEG can go down much quicker than I'd like, which I'll admit can lessen the drama. But on the average, everyone rolls average. That's why it's called average.
And here's another thing. The group I run used to have another DM (he moved away shortly after I joined, so I barely played under him). They consistently took on greater challenges that they should have beaten in his game. And yet, they never had a character death. Never. Yeah, they knew the DM fudged. I mean, it gets obvious when your characters never have a night of bad luck in 5+ years of playing. When I started DMing, I warned them I wouldn't fudge. I asked them what they thought, they said "That sounds excellent!" That very first night, a character died an horrible death. And I've had many others since. And yes, some are anti-climactic, to a degree. Not too long ago, a character died at the bottom of a spiked pit because he rolled a 3 on a jump check. He needed a 5 to make the pit, and he didn't. But they -liked- it. Why? Now they think. When they had to recross the pit, they set up a pulley system, using the tools at hand, instead of just trying to jump the pit, trusting -me- to make sure they wouldn't die. Why bother with a pit trap if no one can ever die from it?
Knowing they -can- die, even in a stupid, unimportant encounter with goblins make the game more fun. It makes tactics more important. Not just avoiding stupid decisions (which should be a given), but striving for -great- decisions. Because they -know- I won't fudge, they do their darndest to put every numerical advantage on their side. And that leads to better roleplay, I think. After all, it's not that great roleplaying to try jumping a pit while wearing heavy armor, no matter the fact that you only need a 5 thanks to your great strenght.
And I'll admit, it makes it more fun for me if I don't know how everything will turn out before game time.