Responsive Design Image Question.

Using the responsive layout on a 1200px screen.

My images are 940px wide and on a 1200 screen only show at 940px wide.

My banner images are 940 wide but will display at 1200 on a 1200 screen.

Shouldn't all of my images display at 1200?

Yea I also noticed this. Can't understand why would cs-cart enlarge or shrink images.