[Why would you do that?]

OP? > I'm surprised by this little drop (not that it'll change the bad overall performance) . Positive news?

A week is 7 days. 7 days * 52 weeks = 364 days. Of course, a year is 365 or 366 days, so there is an extra day or two not accounted for when you count a year as 52 weeks. Those days add up over time, so Famitsu and Media Create need to create a Week 53 from time to time.