My 960 grid system has wider columns that standard. 55px instead 40px for 16 columns
On wide screens, Omega (or in fact: its base theme 'Alpha') will switch to the wide lay-out. You will find the css for it in alpha/css/grid/alpha_default/wide/alpha-default-wide-16.css and alpha/css/grid/alpha_default/wide/alpha-default-wide-12.css.

This responsive behavior can be controlled from the Omega theme settings page.