Good marketing can't be the answer, because their biggest demographic in the south and rural areas nationwide, will be Christians.
They seem to be trying to accomodate the political correctness movement, and there are many on this thread who think that is a good thing.
Speaking as a software QA person I'd guess that making the section Christmas over and above having Christmas in the keywords of so many items hoses up the search engine. Speaking as a person who used to work in retail it could also be organizational, it's possible they recycle the Holiday section on their website for which ever holiday is prominent at the time in much the way the recylce the seasonal section of their stores.
I don't see any accomodations to PC. The Holiday page has the word Christmas on it 5 times, if they were going PC they'd call them "trees" and "bouquets" not "Christmas trees" and "Christmas bouquets". I don't see anybody on this thread that thinks PC Christmas is a good thing, I see lots of people on this thread that look at the WalMart page and don't see any PCing.