False. The main issue with squares is that the 8 directions aren't of the same type. 4 lets you cross a side to another square while 4 lets you cross a corner. The corners then let you move faster (by almost 50%), makes staging an attack from a corner important (as you get less enemy squares to cross), and lets enemies sneak through holes, which needs twice as many units, or a ZOC feature to fix.
Wrong.
In Civ IV, the eight directions are treated as equal, and thus THEY ARE EQUAL.
Diagonal movement does not strictly let you move faster. One square diagonally is exactly as far as one square horizontally or vertically. A target that is five squares north requires five squares of movement. A target that is five squares east is five squares away. A target that is five squares north east is five squares away. All of these distances are the same in game terms.
You can move one square north-east, followed by one square north-west. This is the same as travelling two squares north. You are no further north than you would be is you moved two squares north. Likewise, if you move two squares north-east, you are no more north than if you moved two squares north. Nor are you any more east than if you moved two squares east. You have not moved any further/faster by using diagonals.
The only possible advantage gained from moving diagonally is that it is a straight line if your are trying to reach a target that is in a diagonal direction. Yes, going north east IS quicker than going north and then east. However, this is no different than going directly north to a nothern target is faster than going east and then north, or even north-east then north.
It must be remembered that grid-based systems, whether squares or hexes, are models with built in assumptions. One key assumtion with these is that it does not matter where in the tile an object is - it is always assumed and represented as being in the centre of the tile.
Another assumption is whether or not diagonal movement is identical to non-diagonal movement. This can differ depending on the specific grid, but in Civ IV, we actually see instances where it is treated as identical in some respects (unit movement) but not indentical in others (culture expansion and the BFC). In any model, you are supposed to choose one decision or the other. Many of the issues caused with diagonals come down to the fact that both are being used in the same model. This is NOT an issue of square-based systems, but rather an issue caused to bad game design.
*Hexes increase the number of possible straight fronts from 2 to 3.
*Hexes increase the number of staggered fronts from 2 to 3.
*The issues with staggered fronts are the same with both square and hex based grids.
So basically hexes increase the number of possible fronts on all respect without introducing new issues.
The new issue is that the orientation of the hex matters, and this means that you get situations where a tile can be attacked from the north or south by only two units (excluding ranged bombardments), where as the same tile can be attacked from the east or west by three units (excluding ranged bombardments). Compare this to the square grid where a single tile can be attacked by three tiles in any direction, be it north, east, or north-east.
Ther four cardinal direction of north, south, east, and west are important because they directly correspond to the axes of the typical 2d space that humanity exists in (despite being 3d beings, because we lack the ability to inately travel in the 3d dimension of up and down without aid, these directions are mostly neglected). These directions are much more important to retain, yet instinctive straigh-line movement in at least one axis is lost with hexes.
So, all unit move at least two hexes. But do all units move in exactly even amounts of tiles at all times? What about terrain? Any odd movement value at all precludes the ability to move a front perpendicular in any direction. Thus this remains an issue.
Plus, more fronts is not neccessarily better. Why is having the possibilty of 3 straight fronts and 3 diagonal/staggered fronts better than the possibility of 2 straight fronts and 2 staggered fronts?
Also, you get the fact that even with the straight fronts are the fronts where the tile can only be attacked from two adjacent tiles, and neither of them is directly in front of the front, but instead displaced half a hex to either side.
These are all issues that arise to get rid of the issues sneaking through diagonals that stems from the fact that Civ IV does not follow perfect games design princples such as consistancy within the games rules and models.
Ultimately, either a case of change for change's sake, or throwing the baby out with the bathwater, both of which are not good for the series.