I think you're other response was more accurate, Sony is feeling the heat and doesn't want to lose December by too much.

I also think stores want to move Xmas inventory. 

Thing is, you don't push inventory when you know the console is going to sell.

The entire point of holiday sales is to get people into your store rather than another retailer. That's why gift card bundles are such a huge thing. You want people spending money there. Cutting 70$ off price is pretty major. Retailers make almost nothing on console sales, so basically, these retailers are probably taking somewhere in the area of 50$ loss, which is a pretty big deal when you could just hold. It would be one thing if it was costing them 50$ of profit for the space each ps4 was taking up, but it's very unlikely.

I think the most likely thing is that Sony is supplementing cuts, just like microsoft does. We know that console manufacturers do this already, so it's rather logical to say that these cuts are manufacturer discounts....which means Sony wants marketshare and installbase.