Well, consider this:
The externalization of breasts (i.e. that round, protruding shape off the women's chest that we all know and love) is genetically unnecessary, concerning the practical, biological function of breasts. Breasts are used to feed babies, and (according to unknown sources I vaguely remember), none of the milk-to-nipple production, or storage occurs within the external, rounded, breast - a completely flat chest could be equally proficient in this regard.
Conclusion? The purpose of breasts, in this shape and form, is completely sexual. They evolved to be there specifically for our enjoyment. Breasts actually do exist for the enjoyment of men (and, apparently, Lina).
And, Demonspell, I have no idea why they call it "Pussy"... but then how did "Dick", "Wang", "Schlong", "Willie", etc. all get applied to penis?