From a developers point of view I can say that in certain cases, adding additional options inside of the game sometimes also add another level of abstraction away from the game. In some cases it can make the configuration more confusing but it is not uncommon for the reason to be flawed interaction design and development planning (which, to some extent, i believe is the case in with FFXIV).

Adding things like texturemap quality and texturemap filter to menus inside the game bring with it the need to restart the client executable due to these options fundamental construction. In the case of texture quality and filters there is a need to pre-process/calculate lot's of data prior to showing it on the screen. This is only one of the reasons that putting these kinds of options inside the game may confuse less tech-savvy users and make their game experience less enjoyable.

However, my opinion is that far from all of the settings that are placed in the external configuration tool have a clear motive to their placement. Also, it seems that SE developers often tend to take the "easy way out" when faced with critical software design challenges.

And in closing, obviously ANY setting COULD be implemented inside the game... it's all just a matter of usability, interaction design and budget decisions.

/Gasher