Interesting discussion here. It seems like there are really two separate things people are asking for:
1. A system that has an already given set of fluff, and mechanics, that match up with each other.
2. A system that enables players to take fluff they make up and translate it into mechanics.
---
For (1), threads like these, which provide ideas for fluff that people can put into their games, are very useful. Of course, whether a particular piece of fluff is adequate is completely subjective. For instance, I have no problem with the "fluff explanation" that the reason martial abilities have use restrictions the same as magical abilities is because they are really two different manifestations of the same underlying phenomenon, in the same way that (IRL) electricity and magnetism are two manifestations of the same underlying phenomenon - electromagnetism. I have proffered this explanation in other threads, and have noticed that it is not satisfying to many. There's nothing wrong with this - it's just that different people prefer different fluff.
I will, however, make a few related comments.
1a. Almost all the discussions about 4e fluff not matching up with mechanics tend to mention the same few examples - encounter/daily use restrictions, "physical" forced movement being treated the same way as "mental" forced movement, knocking oozes prone, leader healing abilities like Inspiring Word working on unconscious characters, and of course the old favorite Come and Get It. This means that it might be possible to get rid of most of the problem just by changing a relatively few problematic rules. (I am planning on posting a thread in the 4e House Rules forum about this issue - when I do that I will post a link to it here.)
1b. There were a lot of mechanics that didn't have any kind of "fluff" associated with them - or at best relatively vague and handwavey fluff - in all editions of D+D and probably most other games. How exactly do hit points work? What are you physically doing when you "prepare" a spell? When you use a long-range telepathy spell, how do you designate the target? (Is there a telepathic "phone number"?) What does a character perceive (if anything) at the moment he goes up in level? (Do characters even know what level they are? If not, how do wizards know what types of what level spells they can prepare?)
1c. The kind of "fluff description to justify mechanics" that is being demanded here is often not available even in real life. For example, when I push down on a car's gas pedal, the car accelerates. That's a "mechanic" - when I do this, that happens. What's the "fluff" that justifies this "mechanic"? In order to know that you would have to know how a car's engine works. But of course you don't have to know how a car's engine works in order to drive the car. Most of us do just fine only knowing the "mechanics."
Now let's move on to (2). This is a little more complicated - we now want a system that will enable people to translate their own fluff into mechanics. Let's look at a few different ways of handling this.
2a. One way is the "toolkit system" approach used in systems like HERO/Champions. Systems like these allow you to design your own powers, items, and creatures by giving yo ua language to express abilities in terms of mechanics. For example,
In other words, being able to "build a game model" of a panther or a Panzer and then figure out what "level" it should be is significantly different from having to start with an abstraction and then "skin" it superficially to resemble a mammal or machine.
If you want to "build a game model" of a Panzer in the HERO system, you could do that. You would take each element of the Panzer, decide what it can do, and express that as a power. Main gun? Ranged killing attack, Xd6, armor piercing, takes Y rounds to reload, etc. Armor? Physical defense, value Z. Targeting system? Combat Skill Level that gives +W to attacks with the main gun. Then the system would tell you how many game points each of these are worth, so you give the whole tank a "point value" which is the HERO system's counterpart to "character level."
There's only a couple problems with that:
2a.1. Since you have more freedom in making your own powers, there's a lot more ways to abuse the system. (For instance, I figured out a way to make a power in the HERO System that only costs 70 or so character points but can provide the entire party with 1,100 character points' worth of bonuses to their attributes.) So it still requires DM judgement to outlaw abuses.
2a.2. It doesn't technically solve the original problem, which was to have a system that allows you to input a "fluff" description and receive as output a mechanical description. You still have to convert the fluff into mechanics yourself (in the Panzer example, figure out what X, Y, Z, and W are) - the system just gives you maximum variety in the kind of mechanical descriptions you can come up with, so you can make it match the fluff more closely.
On the other hand, the general idea of a system that "allows you to input a "fluff" description and receive as output a mechanical description" seems to me to be infeasible without a lot of DM fiat. For instance, how would such a system work that would allow you to build a tank like the one above? Presumably it would have to have some way of converting a "fluff description" of the armor (X millimeter thick wall of Y material) into a mechanical description (blocks Z points of damage). In order to be able to do this in a general way it seems like you would have to have a complete model of the world's physics, chemistry, biology, etc.
---
2b. Another approach, that tends to be simpler, is the "abstract model." Systems like these completely separate the fluff from the mechanics. An example is the FATE system. In this system there is a set of general rules for handling a combat, with generic actions (attack, attack but do an effect other than damage, defend, recover, use an aspect to enhance one of the above). Players' decisions still have an impact on the combat, and it's still possible to translate actions ("I push the target out of the way") into mechanical descriptions ("Like a regular attack, except that if you hit the target is out of the combat for one round instead of being wounded") So different actions can end up working differently, but again the translation from "fluff" to "mechanics" still involves DM judgement. It's just that there are a lot fewer complicated rules getting in the way.