What would cause steering wheel vibration and shake at speeds between 70&80 mph?

I am not sure , but will ask them to do so at next service. If it was a suspension component would it not happen at low speeds also? What are]\your thought on it being a warped rotor? Thanks for the reply

Warped rotor won't generally have an effect until the brakes are used, unless you've got a caliper that's not releasing completely.....try this next time. Up at 70 MPH , maintain the vibration with your foot on the gas and GENTLY step on the brake pedal with your left foot , if that stops the vibration , I would lean towards worn suspension.