I personally believe a musician can interact with guests and be inviting while reading music.
"I offer you 5 hours of professional, appropriate, memorized repertoire. You want your professional to interact with your guests, be inviting, approachable, and ensure your guests feel welcome! For weddings/events that may require special music, there would be sheet music on the piano as the only exception."
I also think that musicians nowadays need to be more versatile than ever, and that it isn't a reasonable expectation to request memory at all times from them.
Picture from http://www.youdidntdidyou.com/Photography_Blog/2010/04/22/wynyard-hall-weddings-its-about-the-brides/