User blog comment:DaNASCAT/Technical Update: October 23, 2012/@comment-3441771-20121024031444/@comment-4674838-20121024033931

Changing the gutter doesn't seem to have the best interests of Wikia's new grid layout in mind. For example, if you increase the empty space between between the left and right columns, then the width of left column must decrease from the intended 670px (or else the width of the right column must decrease from the intended 330px).

Changing the width of the right column could make ads render in places they shouldn't. Changing the width of the left column leaves you less room for content and changes those beautiful 160px regions.

Basically, I see this as "10px is meant to work well with grid layout and changing it may have some risks. If you want to mess with that, it's best that you know what you're doing with CSS"