From watching Uptairs Downstair, Boxing Day was set aside for the staff to celebrate, because their services were needed on Christmas Day.
Let's ask snugs!
We have 2 days off at Christmas - Christmas Day and Boxing Day there are many different interpretations of what Boxing day actually means.
I like the one that traditions says that the Lord of the Manor etc boxed up his goodies from Christmas and distributed them to the poor the next day.
The following is a link which explains it more
http://homepages.tesco.net/~derek.berger/holidays/boxingday.html