As I said, I believe it should be a 'featured image' rather than 'best image uploaded this week'. That's what it was since the site was created.
Besides which, the measures you use (the SQL query) will ALWAYS side with an older image (as it will have had more votes if uploaded on the 1st day of the week than the 5th) which means your results will always be skewed.
Before you did IOTW for the 2 weeks, I always treated it as a featured image (I doubt I ever chose one uploaded in that week). I try and choose them from the past 7 days now, but still I don't like the popularity vote as it will never work out properly. The older the image, the more votes it has, thus the more chance of IOTW status. It doesn't work. Plus using that method has resulted in some REALLY fucking crap images being chosen by the system as 10 x 1 vote ranks higher than 9 x 5 votes.
Think of a way to bypass that issue (and no I don't think average votes per day is useful either) & I'll consider it. Until then,