I think that the vast majority of the potential "buyers" are expecting to have a turn based combat system in the vanilla game.
In all likelihood, the vast majority of the potential buyers of Elemental have never heard of the game; and if they have heard of it, they probably only know that it will be a turn-based 4X strategy fantasy game. And when they do hear about it, they will expect whatever kind of combat is advertised.
Those were excellent strategy games [don't get me wrong], but imo a real turn based or tile/turn based system works better in certain games. I think that it is the way to go in a real fantasy TBS game. [Ex.: AoW2-SM or MoM]
The Total War games are "real TBS games". They have been eminently successful without a "real turn based or tile/turn based system." Civilization IV, in fact all of the civ games, are "real TBS games" and they don't even have tactical combat at all. The only reason that they don't fall under your categorization is that they are not fantasy games, but honestly that's a largely cosmetic difference. A game mechanic that works in a historic or otherwise non-fantasy game would work just as well if you modified in some fantasy elements.
It really has nothing to do with "X type of combat is better suited to this type of game than Y type of combat." Pretty much ALL types of combat that have been suggested have been done successfully in some TBS game or another. It is simply a matter of what combat mode will be the most popular, and which the devs think they can do the best and best suit their vision for the game.
How is it realistic to send out your units in a we go system with by nature a limited number of options for the AI, can you really program a unit to think for itself. Really how many games has the AI been a really tough opponent(without cheating)? I spend all the time and effort to craft my kingdom and my military to entrust their defense to a limited computer entity deciding how to carry out an attack. My preference is knowing that I have enough control to accomplish what I want.
How is it realistic for the entire battlefield to wait twiddling their thumbs while it's my Archer Squad #3's turn? How is it realistic for squads of units to only move through squares, and position themselves at large, predetermined locations? WEGO is much more realistic than that: you give commands, which can include "if ___ then ___" scenarios, broad orders like "Defend this unit" or "Defend this location." Even how to defend it (can it use spells? only hand-to-hand? what about special abilities? etc). The AI responsible for carrying out the execution phase of WEGO should be easier to do well than for a full-blown RT system, because it doesn't have to worry about long-term strategy. It requires a tactical AI, while the player is responsible for the overall strategy (obviously, AI players would sitll be responsible for its own strategy, but that is always the case). I would argue that in most games with WEGO combat, you do have enough control to accomplish what you want, unless your opponent outmaneuvers you. I don't see how that could possible be a bad thing.
If we go, and continous real time, and RTS are your what you like, good, there have been hundreds of examples of these made in the last 10 years. This is a good thing because choices and variety are great. But this is the first major game to have TBS tile based combat for close to a decade, I for one am looking forward to it.
People keep saying this, but I don't see it. Straight up RTS games (ala starcraft, age of empires) simply don't count - totally different genre, totally different objectives and significantly different gameplay even regarding the combat aspect. Pretty much every TBS game out there uses regular old turn-based combat (or doesn't have any to begin with) - HoMM, AoW, Civ, King's Bounty, the list goes on - and it is even more extreme when talking about fantasy TBS games. HoMM IV and V, AoW:SM, King's Bounty and King's Bounty: The Armored Princess are 4 major TBS games with TBS tile based combat all within the past decade, some fairly recent. Elven Legacy, too.
What fantasy TBS games are there with any other type of combat besides straight up turn and tile based? King Arthur - it has Total War-like combat. Dominions 3 has scripted WEGO combat. King Arthur was fun, but has a very limited replay value; all it has is the campaign so, even though you have some small control over how things go, it gets old after a couple playthroughs. On the other hand, games like HoMM and AoW:SM have excellent sandbox modes and incredible replayability. Dominions 3, from what I can gather (haven't played it), is a rather extreme form of WEGO combat - you script out everything for the whole battle, and then watch as it plays out. Not necessarily accessible to the masses.
So actually, I would turn your argument around on you - pretty much every fantasy TBS game to date has used regular old turn and tile based combat. The occasional fringe game has broken out of the mold, but are either geared towards a very small demographic (Dom 3) or don't have much replayability (King Arthur).