Just because the tires are new, I wouldn't automatically assume they are balanced correctly. Although I've never run a balancer myself, I'm told a monkey could do it. However, all of the tire monkeys I run across ALWAYS need a second, or even a third chance to get the balance right. Huge pet-peeve of mine. I'm >| |< this close to buying a balancer for my garage... if only my wife wouldn't kill me.
EDIT: If both front tires were out of balance, the vibration in the steering wheel would come and go if you are rounding a turn, as in the long sweepers you'll get at highway speeds. With the outside tire spinning faster than the inside tire, the vibrations in each tire will gradually shift from being exactly synchronized, to being 180° out from one another, then back in sync again.