It's a new year (Gregorian). As it's the 1st January everything that was posted over "2 days ago" now includes the year in the timestamp.
Although it is technically last year, including the year makes it seem, to me, longer ago than it actually was.
Instead of separating posts into this year and last year can the timestamps include the year only as it becomes necessary. So, only those posts posted on 1st January 2012 would include the year in the timestamp. On the 20th June 2013 all posts from before the 20th June 2012 would include the year and all those after would not.
It could also be done on a month-by-month basis.