2" pipe certainly isn't "needed" in most situations, but it is nice to have. It will improve the overall efficiency of your system by several percent, which can add up in electrical savings over the years. Plus, as Isaac-1 said, the additional cost is so small that it is a guaranteed win in the long run.
The "standard" has been moving away from 1 1/2" pipe towards 2" pipe for years. These days more pools are built with 2" than with 1 1/2", though there are still plenty of 1 1/5" pipe pools built.