Two things to think about....well, maybe three...depends on how you look at it.
1. The sugars generated during mashing have only slightly varying solubilities with respect to temperature. It is the physical extraction from the spent grains goop that requires the extra water.
2. Other components released/produced in the mashing process are more temperature dependent with respect to their water solubilities (ie the tannins, proteins, unconverted starches....).
3. The flavor/feel/head/color/clarity/..... of the beer is dependent upon how much of these other components you extract into your wort. Many recommend avoiding high temp, high volume sparges (that people like me are always tempted do to so as to get every last ounce of beer potential) since these tend to result in woody tastes. And, in the end you have to spend time and gas ($) to boil off extra water which really yielded very little extra beer.