We wash our hands twice during the seder. This time, we wash without reciting a blessing. The absence of a blessing here acknowledges that the custom of washing one’s hands before eating vegetables, while once a part of Jewish ritual, is no longer practiced. This hand-washing is a vestige of that custom. We clean our hands here as a preparation for eating, but later in the seder we wash our hands as a spiritual practice, so a blessing is more customary at that time.

haggadah Section: Urchatz
Source: http://jcua.org/document.doc?id=10