Many fuel cells would still use some sort of fossil fuel (Natural Gas is a popular option) instead of pure hydrogen. It pollutes some but is still very clean. The thing about internal combustion is that it is not an especially efficient way to extract energy from fuel. Most of it gets wasted as heat, vibration, noise, etc. With an electric vehicle, you can deliver vast amounts of torque and still get better mileage than with an IC engine. Imagine 1500 HP of instant-on torque, 25 MGP, no noise, and ultra-low emmisions.