What I am saying is to only use the comparison to feet as a guideline, to make sure there is consistency, and then after that point it would become flexible. More than 6 zones away could then be viewed in groups of 6.
Having 1 zone~15' square would allow, for example, the translation of spells more easily simply by rounding. A fireball would hit everyone that is in the same zone. A flame strike (5' radius) could be written as target: 1-2 adjacent creatures.
I understand you are saying that once you place actual measurements on a 'distance' or 'zone' then it becomes much less abstract, although I think you may be overstating the rigidity of the suggestion. IMO if Stormingmarcus is going to base his rules off the SRD and D20, there are just too many things that are tied into measurements to not have some sort of guideline.
I re-read your posts above, and I honestly don't understand how having a guideline for the size of a zone goes against anything in your suggestion. In your version, you are still assuming some sort of continuity for zones: a certain amount of movement to go from one zone to the next, everyone within the same zone is considered adjacent and can melee attack each other. That's all the same.
If we compared it to using 5' squares and a battlemat, then you get into cover and trying to 5' step and flank and all that. Whereas by saying 'everyone in a zone is adjacent' - no matter how big a zone is assumed to be - the party can just say, ok I work my way around so I'm flanking, or I'm going to hop on a table to attack, without worrying exactly where each miniature is.
I would be interested in seeing an example of an in-game situation that you would want to have complete flexibility or that the guideline of having zones be around 15' (i.e. anywhere from 10-20' wide) would be too constricting or hard to keep track of verbally?
You say that to have the guideline of how big a zone is defeats the whole purpose of a zone. What do you see as the purpose of a zone? And why would a guideline of how big that zone is defeat the purpose?
I am asking because I am curious, and it seems you have played without miniatures before so you perhaps have a better understanding of how it works in practice.
Yea I think your right in that using dimensions like feet could help in the design process so other game effects are more balanced...I can't argue with that
To use the idea of 'zones' in a game, I think the whole game would have to be based on this idea, and a whole lot of the tactical element of 20 would have to be changed to compensate for it.
One thing that I think would be kind of neat, and almost impossible to implement, would be a d20 game that catered to both... the Abstract use of just Zones along with the detailed, tactical element of concrete dimensions, and possibly having them overlay each other... but I think that is almost impossible to do.
When using just Zones, the whole paradigm of how a combat would go might have to be changed...you can have a lot of the game mechanics, Feats and Talents and whatever the game will use, but some of the other, more crunchy bits, such as flanking and stuff like that, or anything that miniatures really show, might have to be tossed out the window.
If 4 people are in Zone 2, lets say, then they are all in Zone 2. It doesn't matter where they are in that Zone, but that they are. They are adjacent to each other, and therefore they can pull off combat maneuvers that are based on being adjacent or "in the same Zone." Perhaps Flanking somebody is a unique combat maneuver that you can try to do when "in the same Zone as somebody," and it could be a unique skill check, like Acrobatics. So, you Target somebody, make a Flanking maneuver check, and if you succeed, your gain an immediate single attack against that person as if you are "Flanked" and therefore gain whatever bonuses having Flanking would give you. Flanking would be a temporary condition that would only give this attack and only for the person who made the Flanking check.
All without the use of miniatures.

Of course, you can still use miniatures, just put them in their respective zones but real placement of position doesn't matter.
An example spell, lets say Fireball (we always have to use Fireball at sometime) is a spell that can be cast up to 4 Zones Distance. That's all that needs to be known. And it hits everybody in the target Zone. Everybody in Zone either makes the respective Save, or however its done in your game, and then roll for damage and apply it to everybody in the zone. Actual dimensional size of zone doesn't matter, in this Abstract sense.
Maybe Ghoul Touch is a spell with a range of 0. That means that it can only target someone in the same zone as you, or Zone 0 Distance. Same thing as saying its a Touch spell.
Because of the ever flowing nature of how combat should be, and not the rigid way of how combat has always been made out to be, thinking in terms like this opens it up (in my mind at least) the overall chaotic nature of how combat is more likely to work. In the heat of the moment, it doesn't matter where exactly you are on the map, only that you have a rough estimate of where you are in relation to who you want to attack, and Zones really help visualize this because you aren't as worried about the really specific tactical element of the game anymore... and theoretically this should speed combat up more.