The difference being game designers are often explicitly not trying to do accurate physics. But I don't think most game designers are explicitly not trying to do accurate arithmetic.
When I beta tested Champions Online, I decided to analyze the effectiveness and performance of the defensive powers (of course). I concluded they were wildly unbalanced, and in some cases explicitly broken mechanically. I summarized my observations and sent them to the devs, asking if they wanted to discuss further. I never heard back from them the three separate times I tried. When they launched, players complained they were horribly unbalanced and in some cases broken. The devs posted something that basically said trust us, we have a spreadsheet.
That's when I stopped testing Champions Online. You can't argue with "I have a spreadsheet, ergo I'm right." Even if the math is so horribly wrong that not only can you prove its wrong, you can even prove what must have gone wrong in the sheet without even looking at it (which I posted, then went back to testing combat clocks in City of Heroes and really didn't bother analyzing CO very much past that point).
So many players knew CO, actually, the devs didn't even know the math behind any of the powers they designed. It was blown wide open when people were using power combinations to achieve 10k+ damage hits with attacks that only did around 200-300 damage hits. I remember someone saying to me, "anyone who has any intelligence will leave this game when something better comes along, only people I've talked to who'll stay with this game no matter what were all complete idiots". And I can fully see why the person said that, because when you actually play CO you can definently tell the game is so horribly imbalanced and fundamentally broken that it's more like to scream" build this thing cause it's not only an agro holding tank, it out damages all the damage and only need slight healing in fire and ice!" or "Don't do X because Y does the same thing cheaper, faster and more effectively without any tradeoffs!".
When I look at CO, and city of heroes, I end up respectively looking at Invisible War and the original deus Ex. The original Deus Ex was an awesome game, and certainly earned a lot of respect. City of heroes was the same way as deus ex, an awesome game that earned it's respect. Both games had very solid writing and while they did have problems, they were also well balanced to. JC Denton wasn't a mary sue, he had his faults and it readily became apparent in his dialogue(emotionless, blindly patriotic initially, yet still tended to say something funny once in a while by accident at times).
Invisible war, everyone dispised it. One speed runner described it as a "neat game with a LOT of problems" and most describe it as a linear, generic shooter that marked the beginning of the decline of first person shooters, it lowered the fps standard severely. The story writing was poor, at best, at worst Alex D is very mary/marty sueful, in that he/she is the sole peice of the puzzle EVERY SINGLE FACTION NEEDS. NPCs are even dumber in invisible war, to, the game has less options as well. Even in a case where someone did once try to be a 100% pacifist, he felt the game litterally had no thinking behind it, unlike the original, to.
And Champions online makes very similar mistakes.
It gives a very bad example as to what a super hero mmorpg could be like, in which everyone is a mary sue, just like invisible war's alex D is a mary sue(there are litterally NO consequences for your actions in invisible war, none, zip, zilch, every single faction INSTANTLY forgives anything you do in it no matter how monstrous it is). NPCs worship you in an especially creepy way in CO, the freeform system screams only use the best, story writing is bad, you name it. There really isn't much thinking, other than the character build, and it's easy to fall asleep playing it even.
CO's biggest problem perhaps was developers just running loose with just messing up what makes an rpg good, failing even what it'd really take to make an mmorpg good consequently. I should bring up that video where a guy found out you could become 100% invincible in the game due to a glitch, or the same guy acheving I think 100k damage hits on enemies.
