Anyone else notice this?

I've had several months recently in which sales start out strong, then about half-way through, I see a significant drop in sales.  A later week in the month runs about 30% lower than an earlier week, then when the next month starts, the first few weeks shoot back up and usually beat the first weeks of the prior month.  It's happened enough that I think there's a definite pattern here, but I haven't seen it discussed in the forums, unless I've missed a thread.

Wondering if this is a subscription-based pattern.  If a subscriber is allowed a certain number of downloads a month, and half-way through runs out of credits, he/she may wait until the start of the next month to download more images. 

Thoughts?

I've noticed that too... That makes sense Borg!