Thanksgiving by the Party of First Part to the Creator, Hereinafter Referred to as the "Big Cheese"

The legalities of Thanksgiving are somewhat odd. Under Title 5, Section 6103 of the U.S. Code, it is officially a federal work holiday (http://www.law.cornell.edu/uscode/5/usc_sec_05_00006103----000-.html). In addition, the President also proclaims Xgiving a holiday, as he did this year: http://www.whitehouse.gov/news/releases/2008/11/20081121-8.html. Now, I understand that, before the statute, a presidential proclamation was necessary. Famously, Jefferson refused to issue such proclamations, believing in a strict separation of Church and State. Ain't no federal functionary gonna declare gratitude to the almight on his watch, nosiree. But now, when there is a statute stating that Thanksgiving is a federal holiday, does the proclamation serve any legal purpose?