It is customary to use a smaller needle for sweater ribbing; you will see this in most sweater styles and patterns. A smaller needle ensures a tidy ribbed edge and you'll find that it does not draw inward as much as you might think. When you finish your sweater, be sure to wet block it and draw out the ribbed edges so they are even with the rest of the sweater and pin them flat to dry. The end result is a sweater with a professional edge that enhances the look and fit of your sweater.

Using a larger needle for ribbing or trying to work your ribbing more loosely will often result in your ribbed edge rolling, looking unprofessional, and/or not laying flat - I do not recommend using the same size needle as the rest of the sweater unless a pattern specifically tells you to do so. 

Too often knitters lean toward a looser ribbing (erring on the side of using a larger needle or trying to make it stretchy or loose) because they're worried about it clinging to their figure. I recommend trusting the pattern, knowing that each detail is very specifically designed for best results.