Yes, but stores start selling the artifical ones in October.
I'd say it is the Christians that happily participate in the spending orgy that has become Christmas beginning in October. How many posts were there in the week before Thanksgiving complaining about not hearing Merry christmas from clerks in stores? That indicates to me that Christians are out there in the sores taking part.
I think part of the reason one sees Happy Holidays signs in stores instead of Christmas signs is because they start the sales and we start the shopping so early. Merry Christmas signs look silly before Halloween and diminish the importance of Thanksgiving. Happy Holidays allows them to cover the entire period from Halloween to the BCS championship without changing signage.