Actually, Esana, the eyes are on the same scale in both shots. It's just what our brains have come to expect from that art style. There is a notable difference in that even on the anime girl, the iris and pupils are still bigger. On a different note, this could make for a pretty kick-ass optical illusion, similar to how we're used to seeing italics slanted a particular direction to the point that when they're slanted the other way, it looks like a more drastic angle.
To answer your question, Lukisod, the reason anime eyes are drawn so large is because of the Japanese belief that the eyes are the windows to the soul and are capable of the most expression, and to an extent this is true. For example, you can tell genuine happiness from a fake smile by looking for crow's feet in the outer corners of the eyes. Exaggerating eye size to this extent allows for a greater variety of expression in the art style, especially given the proportionately smaller nose and mouth. (Note also how eyebrows are drawn over the bangs.) There's also less sclera--the white of the eye--on the anime girl. Thus, someone in anime can literally get a twinkle in their eye.
Other differences can be seen in head and face shape. The trend in most anime and manga is to lean towards a wider face in proportion to its height (the better to incorporate those eyes), and even this rule can be bent or broken depending on the desired feel of the character.
Manga is a popular enough art style by this point that guides on how to draw it are popping up in most bookstores and/or libraries, so for a detailed study of the differences between this medium and reality, I suggest picking up a couple of those for further insights.
How long will he keep on fighting? How long will his pain last? Maybe only the X-Buster on his hand knows for sure...