And in previous editions, yeah, it does create a problem.
Err... I don't know what problem or previous edition you are talking about, but whatever you mean by it, it doesn't seem to be be a logical responce to what I just wrote. In fact, it seems to me to be the opposite of understanding what I wrote.
Depends on the character. If your game, in the city, the mountains, or other locations, pits the characters who rely on armor at a disadvantage in terms of how easy they are hit or suffer damage...
You just don't get it. I mean, this is just one of a long series of statements that are just utterly backwards. Characters who rely on armor ought be at an advantage in terms of how easy they are hit or suffer damage compared to those that don't rely on armor. Conversely, those who don't rely on armor are at various advantages in terms of mobility compared to those who do. If those that wear armor have no advantage in protection, why would they wear it? And if wearing armor caused you no disadvantage in mobility, why would you not wear it?
If the Game Master wants to 'ambush' the players in town...
Again, you just don't get it. I want to be entertained. I don't want 'to ambush' players. I rather dislike 'ambush' to begin with. If more than 1:4 or 1:5 encounters are ambushes, you are probably doing something wrong. What happened to meeting engagements, or does the villain have some supernatural sense of where the PC's are at all times and spends every moment waiting for them to show up?
Players may or not be ambushed in town or out depending on their choices and the advantages or disadvantages of their character. I don't have some prearranged story that includes 'ambush in town', and if I do have an encounter in mind that involves 'ambush in town' it will probably - barring really bad choices by the player - be one which I expect the players and their characters to have the resources at their disposal to win (or at least survive) and that will include my calculation about the availability of armor.
Not at all. I'm stating that if you punish the people wearing armor by putting them at a disadvantage, the players will make characters that do not rely on it.
What makes you think I'm putting them at a disadvantage? I'm not putting them at anything. Presumably, characters take their armor off because they realize it puts them at an advantage, and put it back on for the same reason. Again, I don't think you even get it. Didn't I rip apart the entire approach of, "Try to get the PC's to take their clothes off in order to ambush them." Yes, occasionally if you take your armor on and off rather than living in it 24 hours a day, you might find yourself fighting defensively/using the expertise feat/etc. when you might otherwise have prefered your armor, but what of it? You'll still probably rip apart whatever it is you are fighting, because, dude - you are a hero and the bad guys probably aren't clanking around in plate mail either.
How do those 'physics' handle falling?
In my case, with a handful of d20's, a d6, some modifiers, and likely a massive damage save. Alot of effort over the years has gone into modelling falling, and there is bound to be a system that achieves the level of versimilitude you are looking for.
How do those 'physics' handle disease?
As a reoccurring saving throw with temporary attribute loss and some associated symptoms. I made a rather complex disease system in 1e, but I think the 3e edition system is on the whole a good starting basis and you can add whatever detail you feel is lacking.
It's a game first and foremost and when you put the players, who are NOT standard inhabitants of the game setting into situations where they are punished for wearing armor, they will take classes that do not rely on it.
In which case, they will be 'punished' when they get into game situations where you are 'punished' for not wearing armor - like I don't know, when the angry bugbear warband is trying to smash you flat with mauls or shoot you full of arrows fired from great bows. I suppose it is true that if I ran a desert focused campaign or nautical campaign (ran one and been a player in the other) that most people will find some alternative to heavy armor regardless of class, just because, for example, being strapped into to 60 lbs. of steel when you fall off a boat in 6000' feet of water is usually bad. Even if you manage to rip the buckles off, you are still losing that +4 plate mail. However, that doesn't mean that you don't own armor. You just don't wear it aboard the boat or anywhere else it doesn't make sense. And yes, if you are in a campaign where heavy armor doesn't make sense, you'll try to grow your character's abilities and gear to suit that situation. I wouldn't normally plan on wearing plate in a campaign that was centered on the jungle or desert, although I might consider that line of play opened up for me if I found a magic item that let me endure high temperatures.
And in terms of denizens shunning armor... don't the vast majority of 'normal' denizens do that already? The players, NOT standard inhabitants, have funds, training, and other advantages that the normal denizens do not have access to.
Sorta. For example, your Paladin might get a
ring of water breathing, which makes wearing armor aboard a ship a bit less suicidal. Also, that Paladin maybe has a +20 swim check, allowing them to heroically swim (if just barely) with 100 lbs of dead weight. But these are ways to compensate for the inherent disadvantages of armor; they don't elimenate their existence.